System and method for selective and maintained activation of sensory peripheral nerve fibers

ABSTRACT

Electrical stimulation is applied to a patient at least in part via a pulse generator. A motor fiber component of an action potential that is evoked in response to the electrical stimulation is measured. A sensory fiber component of the action potential is also measured. A relationship between the motor fiber component and the sensory fiber component is determined. For example, a ratio between the sensory fiber component and the motor fiber component may be calculated, or the absolute sizes of the sensory fiber component and the motor fiber component may be compared. Based on the determined relationship between the motor and sensory fiber components, a paresthesia of the patient is estimated.

PRIORITY DATA

The present application is a continuation application of U.S. patentapplication Ser. No. 14/321,914, filed Jul. 2, 2014, which is a utilityapplication of provisional U.S. Patent Application No. 61/841,965, filedon Jul. 2, 2013, entitled “Stimulation Apparatuses, Devices, Systems,and Methods,” the disclosures of each are hereby incorporated byreference in their entirety.

FIELD

Various embodiments described herein relate to the field of implantablemedical devices, and methods of communicating therewith.

BACKGROUND

As medical device technologies continue to evolve, neurostimulatordevices have gained much popularity in the medical field.Neurostimulator devices are typically battery-powered devices that aredesigned to deliver electrical stimulation to a patient. Through properelectrical stimulation, the neurostimulator devices can provide painrelief for patients. In effect, the electrical signals sent by theneurostimulator devices “mask” or modify the pain signals before thepain signals reach the patient's brain. As a result, the patient mayfeel only a tingling sensation (known as “Paresthesia) in the area thatis stimulated instead of pain. For example, peripheral nerve stimulationhas been used to treat chronic pain emanating from a patient'sextremity, such as in the patient's arm and/or leg. A typical peripheralneurostimulator (PNS) device may include one or more integrated circuitchips containing the control circuitry and neurostimulation circuitry.The PNS device may also include a plurality of electrodes that are incontact with different areas of a patient's body. The PNS devicetypically includes a battery, either permanent or rechargeable, that isutilized to power the stimulation circuitry and the externalcommunications. Controlled by the control circuitry within theneurostimulator, the electrodes are each capable of deliveringelectrical stimulation to their respective target contact areas. Thus,the patient can use the PNS device to stimulate areas in a localizedmanner.

In spite of recent advances, conventional PNS devices still have variousshortcomings. As an example, the nerves in a spinal cord are typicallyarranged more orderly and run along a linear path, whereas the nerves tobe stimulated in peripheral nerve stimulation usually wind tortuouslyalong a neurovascular bundle. Therefore, a typical paddle lead for aconventional PNS device or for spinal cord stimulation does not offerthe flexibility and versatility needed to stimulate the target nervefibers for peripheral nerve stimulation, as they are not configured toallow electrical stimulation energy to follow the tortuous peripheralnerve targets selectively. As another example, conventional PNS devicestypically require an antenna to receive telemetry signals and a separatecharging coil to receive charging signals. As a result, PNS design ismore complex and more expensive. As yet another example, conventionalPNS devices typically do not employ sophisticated power maximizationtechniques to reduce power consumption. Consequently, conventional PNSdevices tend to have battery life that does not last as long as desired.The short battery life may lead to user dissatisfaction. As yet anotherexample, it may be difficult to determine a target nerve site forapplying stimulation. As a further example, conventional PNS devices maynot be able to provide a constant paresthesia intensity to account forpatient movements. As yet a further example, conventional methods andsystems may not be able to quickly devise a stimulation protocol thateffectively treats the patient.

As a result, although existing systems and methods of peripheralneurostimulation have been generally adequate for their intendedpurposes, they have not been entirely satisfactory in every aspect.

SUMMARY

One aspect of the present disclosure involves an implantable leadconfigured to deliver an electrical stimulation therapy for a patient.The lead includes an elongate lead body that is configured to be coupledto a pulse generator that generates electrical stimulations pulses aspart of the electrical stimulation therapy. The lead also includes apaddle coupled to the lead body. The paddle contains a plurality ofelectrodes that are each configured to deliver the electricalstimulation pulses to the patient. The plurality of electrodes isarranged into at least three columns that each include a respectivesubset of the electrodes. The plurality of electrodes each includes aunique centerline, wherein the centerlines extend in directionstransverse to the columns.

Another aspect of the present disclosure involves an implantable leadconfigured to deliver an electrical stimulation therapy for a patient.The lead includes an elongate lead body that is configured to be coupledto a pulse generator that generates electrical stimulations pulses aspart of the electrical stimulation therapy. The lead also includes apaddle coupled to the lead body. The paddle contains a plurality ofelectrodes that are each configured to deliver the electricalstimulation pulses to the patient. The plurality of electrodes each havea respective first centerline extending along a first direction and arespective centerline extending along a second direction different fromthe first axis. A substantial majority of the first centerlines are notaligned in the first direction with any of the other first centerlines.A substantial majority of the second centerlines are not aligned in thesecond direction with any of the other second centerlines.

Yet another aspect of the present disclosure involves an implantablelead configured to deliver an electrical stimulation therapy for apatient. The lead includes an elongate lead body that is configured tobe coupled to a pulse generator that generates electrical stimulationspulses as part of the electrical stimulation therapy. The lead alsoincludes a paddle coupled to the lead body. The paddle contains aplurality of electrodes that are each configured to deliver theelectrical stimulation pulses to the patient. The electrodes collectivedefine a stimulation region on the paddle. A substantial majority oflinear paths across the stimulation region intersect with at least oneof the electrodes.

Another aspect of the present disclosure involves a medical device forproviding an electrical stimulation therapy for a patient. The medicaldevice includes a coil configured to receive both inductive chargingsignals and telemetry signals. The inductive charging signals are in afirst frequency band. The telemetry signals are in a second frequencyband that is substantially higher than the first frequency band. Themedical device includes inductive charging circuitry configured toprovide electrical power to the medical device via the inductivecharging signals. The medical device includes telemetry circuitryconfigured to conduct telecommunications with external device via thetelemetry signals. The medical device includes a first component that iselectrically coupled between the coil and the inductive chargingcircuitry. The first component is configured to allow the inductivecharging signals to pass through. The medical device includes a secondcomponent that is electrically coupled between the coil and thetelemetry circuitry. The second component is configured to substantiallyblock the inductive charging signals while allowing the telemetrysignals to pass through.

Another aspect of the present disclosure involves a medical system forproviding an electrical stimulation therapy for a patient. The medicalsystem includes an electronic programmer configured to generate firsttelemetry signals that contain stimulation programming instructions foran implantable pulse generator (IPG) and second telemetry signals forwaking up the IPG. The medical system includes the IPG configured togenerate electrical pulses in response to the stimulation programminginstructions. The IPG contains an antenna configured to receive thefirst telemetry signals, the second telemetry signals, and inductivecharging signals. The inductive charging signals are in a firstfrequency band, the first telemetry signals are in a second frequencyband that is substantially higher than the first frequency band, and thesecond telemetry signals are in a third frequency band that issubstantially higher than the second frequency band. The IPG contains aninductive charging circuitry configured to provide electrical power tothe medical device via the inductive charging signals. The IPG containstelemetry circuitry configured to conduct telecommunications withexternal device via the telemetry signals. The IPG contains a firstcircuit that is electrically coupled between the antenna and theinductive charging circuitry. The first circuit contains one or moreelectronic components that create a resonant frequency centered aroundthe first frequency band. The IPG contains a second circuit that iselectrically coupled between the antenna and the telemetry circuitry.The second circuit is configured to substantially reject the inductivecharging signals and the second telemetry signals while allowing thefirst telemetry signals to pass through. The IPG contains a thirdcircuit that is electrically coupled between the antenna and thetelemetry circuitry and in parallel with the second circuit. The thirdcircuit is configured to reject the inductive charging signals and thefirst telemetry signals while allowing the second telemetry signals topass through.

Another aspect of the present disclosure involves a method of providingdiscrimination for a plurality of types of input signals received from asingle antenna. The method includes receiving, via the single antenna,inductive charging signals and first telemetry signals. The inductivecharging signals are in a first frequency band, the first telemetrysignals are in a second frequency band that is substantially higher thanthe first frequency band. The method includes generating, via a firstcircuit coupled to the single antenna, a resonant frequencysubstantially near the first frequency band such that the first circuitallows the inductive charging signals to pass through while attenuatingthe first telemetry signals. The method includes rejecting, via a secondcircuit coupled to the single antenna, the inductive charging signalswhile allowing the first telemetry signals to pass through.

Another aspect of the present disclosure involves a medical device forproviding an electrical stimulation therapy for a patient. The medicaldevice includes telemetry circuitry configured to receive programminginstructions via telecommunications conducted with an electronicprogrammer. The medical device includes stimulation circuitry configuredto provide, in response to the received programming instructions, aplurality of electrical pulses to be delivered to the patient as a partof the electrical stimulation therapy. The stimulation circuitrycontains a microcontroller configured to generate the electrical pulses.Each electrical pulse includes a primary phase, an interphase after theprimary phase, and a recovery phase after the primary phase. Consecutiveelectrical pulses are separated by a standby period. The medical deviceincludes power supply circuitry configured to provide electrical powerto the telemetry circuitry and the stimulation circuitry. Themicrocontroller is configured to operate in an active mode during atleast one of: the primary phase and the interphase, and themicrocontroller is configured to operate in a power-conservation modeduring a substantial majority of the standby period. The microcontrollerconsumes substantially less power when operating in thepower-conservation mode than in the active mode.

Another aspect of the present disclosure involves a medical system forproviding an electrical stimulation therapy for a patient. The medicalsystem includes an electronic programmer configured to generatestimulation programming instructions for an implantable pulse generator(IPG). The medical system includes the IPG. The IPG comprises telemetrycircuitry configured to receive the programming instructions viatelecommunications conducted with the electronic programmer. The IPGcomprises stimulation circuitry configured to provide, in response tothe received programming instructions, a plurality of electrical pulsesto be delivered to the patient as a part of the electrical stimulationtherapy. The stimulation circuitry contains a microcontroller configuredto generate the electrical pulse. Each electrical pulse includes aprimary phase, an interphase after the primary phase, and a recoveryphase after the primary phase. Consecutive electrical pulses areseparated by a standby period. The IPG comprises power supply circuitryconfigured to provide electrical power to the telemetry circuitry andthe stimulation circuitry. The microcontroller is configured to operatein an active mode during at least one of: the primary phase and theinterphase, and the microcontroller is configured to operate in apower-conservation mode during a substantial majority of the standbyperiod. The microcontroller consumes substantially less power whenoperating in the power-conservation mode than in the active mode.

Another aspect of the present disclosure involves a method of providingan electrical stimulation therapy for a patient. The method includesreceiving programming instructions from an electronic programmer. Themethod includes generating, via a microcontroller and in response to thereceived programming instructions, a plurality of electrical pulses tobe delivered to the patient as a part of the electrical stimulationtherapy. Each electrical pulse includes a primary phase, an interphaseafter the primary phase, and a recovery phase after the primary phase.Consecutive electrical pulses are separated by a standby period. Thegenerating of the electrical pulses comprises: operating themicrocontroller in an active mode during at least one of: the primaryphase and the interphase, and operating the microcontroller in apower-conservation mode during a substantial majority of the standbyperiod. The microcontroller consumes substantially less power whenoperating in the power-conservation mode than in the active mode.

Yet another aspect of the present disclosure involves a medical devicefor providing an electrical stimulation therapy for a patient. Themedical device includes a microcontroller configured to generate aplurality of electrical pulses and a control signal. The medical deviceincludes a stimulation driver coupled to the microcontroller. Thestimulation driver is configured to amplify the electrical pulses intoamplified electrical pulses to be delivered to the patient as a part ofthe electrical stimulation therapy. The medical device includes abattery configured to supply a first voltage. The medical deviceincludes a voltage up-converter coupled between the battery and thestimulation driver. The voltage up-converter is configured to convert,in response to the control signal from the microcontroller, the firstvoltage to a compliance voltage for the stimulation driver. Thecompliance voltage is a fraction of the first voltage, and the fractionis greater than 1.

Yet another aspect of the present disclosure involves a medical systemfor providing an electrical stimulation therapy for a patient. Themedical system includes an electronic programmer configured to generatestimulation programming instructions for an implantable pulse generator(IPG). The medical system includes the IPG configured to provide, inresponse to the stimulation programming instructions, stimulation pulsesto be delivered to the patient as a part of the electrical stimulationtherapy. The IPG contains a microcontroller configured to generate aplurality of electrical pulses and a control signal. The IPG contains astimulation driver coupled to the microcontroller, the stimulationdriver being configured to amplify the electrical pulses into thestimulation pulses. The IPG contains a battery configured to supply afirst voltage. The IPG contains a voltage up-converter coupled betweenthe battery and the stimulation driver. The voltage up-converter isconfigured to convert, in response to the control signal from themicrocontroller, the first voltage to a compliance voltage for thestimulation driver. The compliance voltage is a fraction of the firstvoltage, the fraction is greater than 1.

Yet another aspect of the present disclosure involves a method ofproviding an electrical stimulation therapy for a patient. A pluralityof electrical pulses and a control signal are generated via amicrocontroller. A first voltage is supplied via a battery. In responseto the control signal, the first voltage is converted via the voltageup-converter to a compliance voltage. The compliance voltage is afraction of the first voltage, and the fraction is greater than 1. Thecompliance voltage is provided to a stimulation driver. The plurality ofelectrical pulses is amplified via the stimulation driver into amplifiedelectrical pulses to be delivered to the patient as a part of theelectrical stimulation therapy.

Yet another aspect of the present disclosure involves a method ofidentifying a location for applying a stimulation therapy to treat apatient. A first body region of the patient is stimulatedtranscutaneously via a stimulus generator. The body region contains afirst portion of a nerve that has an elongate shape. In response to thestimulating, action potentials received from a second portion of thenerve are monitored over a period of time. The second portion of thenerve is in a second body region of the patient that is located remotelyfrom the first body region. Based on the monitoring, an optimizedlocation of the second portion of the nerve is determined for applyingthe stimulation therapy to treat the first body region.

Yet another aspect of the present disclosure involves a method ofidentifying a location for applying a stimulation therapy to treat apatient. A first body region of the patient is stimulatedtranscutaneously via an external pulse generator (EPG). The body regioncontains a first portion of a nerve that has an elongate shape. Atrigger signal is sent to a measurement instrument. The trigger signaldefines a time window for making a measurement. A plurality of differentaction potentials is measured via the measurement instrument. Themeasuring is performed in response to a plurality of engagements withdifferent fascicles of a second portion of the nerve while the firstbody region is stimulated. The second portion of the nerve is in asecond body region of the patient that is located remotely from thefirst body region. The measuring is performed within the time windowdefined by the trigger signal. In some embodiments, the steps of themethod are performed while the patient is sedated.

Yet another aspect of the present disclosure involves a medical system.The medical system includes a stimulus generator configured to applystimulation to a first body region of the patient transcutaneously. Thebody region contains a first portion of an elongate nerve. The medicalsystem includes a tool configured to engage with a second portion of thenerve that is in a second body region of the patient that is locatedremotely from the first body region. The tool is configured to receiveaction potentials from the second portion of the nerve in response tothe stimulation at the first body region of the patient. The toolincludes one of: a seeking needle or a paddle lead. The medical systemalso includes a measurement instrument electrically coupled to the tooland configured to measure and analyze the action potentials received bythe tool.

Yet another aspect of the present disclosure involves a method ofproviding a stimulation therapy to a patient. A first calibrationprocess is performed in a first patient posture state. The firstcalibration process associates a sensation experienced by a patient, inthe first patient posture state, with a first amount of an evokedpotential and a first value of a stimulation parameter for thestimulation therapy to achieve the first amount of evoked potential. Asecond calibration process is performed in a second patient posturestate. The second calibration process associates the sensationexperienced by a patient, in the second patient posture state, with asecond amount of the evoked potential and a second value of thestimulation parameter for the stimulation therapy to achieve the secondamount of evoked potential. After the first and second calibrationprocesses have been performed, a current patient posture state isdetected. If the current patient posture state is detected as the firstpatient posture state, the stimulation therapy is applied to the patientusing the first value of the stimulation parameter as an initial value.If the current patient posture state is detected as the second patientposture state, the stimulation therapy is applied to the patient usingthe second value of the stimulation parameter as the initial value.

Yet another aspect of the present disclosure involves a medical systemfor stimulating a patient. The medical system includes an electronicstorage configured to store: an association of a sensation experiencedby the patient in a first patient posture state with a first amount ofan evoked potential and a first value of a stimulation parameter for astimulation therapy to cause the first amount of evoked potential; andan association of a sensation experienced by the patient in a secondpatient posture state with a second amount of the evoked potential and asecond value of the stimulation parameter for the stimulation therapy tocause the second amount of evoked potential. The medical system includesone or more sensors configured to detect a present patient posturestate. The medical system includes a microcontroller coupled to the oneor more sensors and the electronic storage. The medical system includesstimulation circuitry configured to generate, in response toinstructions from the microcontroller: a first stimulation therapy usingthe first value as an initial value of the stimulation parameter inresponse to a detection of the patient being in the first patientposture state; and a second stimulation therapy using the second valueas the initial value of the stimulation parameter in response to adetection of the patient being in the second patient posture state.

Yet another aspect of the present disclosure involves a medical devicefor providing a stimulation therapy to a patient. The medical deviceincludes an electronic storage storing respective results of a firstcalibration process and a second calibration process. The result of thefirst calibration process associates a sensation experienced by thepatient, in a first patient posture state, with a first amount of anevoked potential and a first value of a stimulation parameter for thestimulation therapy to achieve the first amount of evoked potential. Theresult of the second calibration process associates the sensationexperienced by the patient, in a second patient posture state, with asecond amount of the evoked potential and a second value of thestimulation parameter for the stimulation therapy to achieve the secondamount of evoked potential. The medical device includes one or moresensors configured to detect a current patient posture state. Themedical device includes a microcontroller coupled to the electronicstorage and to the one or more sensors. The medical device includesstimulation circuitry configured to generate the stimulation therapy tobe delivered to a nerve site of the patient in response to instructionsfrom the microcontroller in a manner such that: the stimulation therapyis generated using the first value as an initial value of thestimulation parameter in response to the first patient posture statebeing detected as the current patient posture state; and the stimulationtherapy is generated using the second value as the initial value of thestimulation parameter in response to the second patient posture statebeing detected as the current patient posture state.

Yet another aspect of the present disclosure involves a method ofestablishing a stimulation treatment protocol for a patient. The methodincludes delivering electrical stimulation to a nerve site of thepatient. The electrical stimulation is delivered using a stimulationconfiguration with respect to one or more of the following: activationof a subset of a plurality of electrodes on a lead, electrode polarityfor the activated electrodes, stimulation pulse width, and stimulationpulse amplitude. An action potential evoked from the nerve site inresponse to the electrical stimulation is measured. The action potentialincludes a sensory fiber contribution and a motor fiber contribution.Both the sensory fiber contribution and the motor fiber contribution aremeasured. The delivering and the measuring are repeated for a pluralityof cycles. Each cycle is performed using a different stimulationconfiguration. The stimulation configuration that offers a greatestsensory fiber contribution relative to the motor fiber contribution isrecommended as a candidate for optimized stimulation configuration.

Yet another aspect of the present disclosure involves a medical systemfor establishing a stimulation treatment protocol for a patient. Themedical system includes a stimulation component configured to deliverelectrical stimulation to a nerve site of the patient. The electricalstimulation is delivered using a stimulation configuration with respectto one or more of the following: activation of a subset of a pluralityof electrodes on a lead, electrode polarity for the activatedelectrodes, stimulation pulse width, and stimulation pulse amplitude.The medical system includes a measurement component configured tomeasure an action potential evoked from the nerve site in response tothe electrical stimulation. The action potential includes a sensoryfiber contribution and a motor fiber contribution. The measurementcomponent is configured to measure both the sensory fiber contributionand the motor fiber contribution. The medical system includes aprocessor component. The processor component is configured to instructthe stimulation component and the measurement component to repeat thedelivering of the electrical stimulation and the measurement of theaction potential for a plurality of cycles. Each cycle is performedusing a different stimulation configuration. The processor component isconfigured to thereafter recommend, as a candidate for optimizedstimulation configuration, the stimulation configuration that offers agreatest sensory fiber contribution relative to the motor fibercontribution.

Yet another aspect of the present disclosure involves a medical devicefor establishing a stimulation treatment protocol for a patient. Themedical device includes stimulation circuitry configured to deliverelectrical stimulation to a nerve site of the patient. The electricalstimulation is delivered using a stimulation configuration with respectto one or more of the following: activation of a subset of a pluralityof electrodes on a lead, electrode polarity for the activatedelectrodes, stimulation pulse width, and stimulation pulse amplitude.The medical device includes measurement circuitry configured to measurean action potential evoked from the nerve site in response to theelectrical stimulation. The action potential includes a sensory fibercontribution and a motor fiber contribution. The measurement circuitryis configured to measure both the sensory fiber contribution and themotor fiber contribution. The medical device includes controllercircuitry. The controller circuitry is configured to instruct thestimulation circuitry and the measurement circuitry to repeat thedelivering of the electrical stimulation and the measurement of theaction potential for a plurality of cycles. Each cycle is performedusing a different stimulation configuration. The controller circuitry isconfigured to thereafter recommend, as a candidate for optimizedstimulation configuration, the stimulation configuration that offers agreatest sensory fiber contribution relative to the motor fibercontribution.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. In the figures, elements having thesame designation have the same or similar functions.

FIG. 1 is stylized overview of the human nervous system.

FIG. 2 is a simplified block diagram of an example medical systemaccording to various embodiments of the present disclosure.

FIGS. 3A-3B illustrate stylized views of various portions of the humanbody with example peripheral neurostimulators implanted according toembodiments of the present disclosure.

FIGS. 4-5 illustrate an example peripheral neurostimulator according toan embodiment of the present disclosure.

FIGS. 6A-6C illustrate an example programmer for a neurostimulatoraccording to an embodiment of the present disclosure.

FIG. 7 illustrates a simplified block diagram of an example peripheralneurostimulator according to an embodiment of the present disclosure.

FIG. 8 is a legend showing how the FIGS. 8A-8L are arranged together.FIGS. 8A-8L illustrates a circuit schematic of the peripheralneurostimulator of FIG. 7 according to an embodiment of the presentdisclosure.

FIG. 9 illustrates example peripheral nerve bundles being stimulated bya paddle lead according to an embodiment of the present disclosure.

FIGS. 10-14 illustrate example paddle leads for delivering electricalstimulation to peripheral nerve according to various embodiments of thepresent disclosure.

FIGS. 15A-15C illustrate a conductive element used by a peripheralneurostimulator according to various embodiments of the presentdisclosure.

FIG. 16 illustrates a simplified block diagram of components of theperipheral neurostimulator used to provide signal discriminationaccording to various embodiments of the present disclosure.

FIG. 17 illustrates circuit schematics of the various components of theperipheral neurostimulator used to provide signal discriminationaccording to an embodiment.

FIG. 18 is a simplified flowchart illustrating a method of providingdiscrimination for a plurality of types of signals received from asingle conductive element according to an embodiment of the presentdisclosure.

FIG. 19 illustrates the power-reduction approaches employed by aperipheral neurostimulator during a passive recovery stimulation pulseaccording to an embodiment of the present disclosure.

FIG. 20 illustrates the power-reduction approaches employed by aperipheral neurostimulator during an active recovery stimulation pulseaccording to an embodiment of the present disclosure.

FIG. 21 is a simplified flowchart illustrating a method of reducingpower consumption for a peripheral neurostimulator according to anembodiment of the present disclosure.

FIGS. 22A-22C illustrate circuit schematics of portions of a voltageup-converter for providing a compliance voltage according to anembodiment of the present disclosure.

FIG. 23 is a circuit schematic of a charge pump chip according to anembodiment of the present disclosure.

FIGS. 24-26 illustrate various simplified timing graphs for signalwaveforms associated with the voltage up-converter of FIGS. 22A-22Caccording to embodiments of the present disclosure.

FIG. 27 is a simplified flowchart illustrating a method of providingelectrical stimulation therapy for a patient according to an embodimentof the present disclosure.

FIGS. 28-30 illustrate a medical system (or parts thereof) for finding atarget nerve site for applying stimulation according to embodiments ofthe present disclosure.

FIG. 31 is a simplified flowchart illustrating a method of identifying alocation for applying a stimulation therapy to treat a patient accordingto an embodiment of the present disclosure.

FIGS. 32A-32C are simplified waveforms that provide an example contextof one or more calibration processes of the present disclosure.

FIG. 33 illustrates a plurality of example patient posture statesaccording to some embodiments of the present disclosure.

FIG. 34 is a simplified flowchart illustrating a method of providing astimulation therapy to a patient according to an embodiment of thepresent disclosure.

FIG. 35 is a graph illustrating several action potentials according tovarious aspects of the present disclosure.

FIG. 36 is a graph illustrating two time windows for measuring a motorfiber contribution and a sensory fiber contribution to an actionpotential according to an embodiment of the present disclosure.

FIG. 37 illustrates an example paddle lead according to an embodiment ofthe present disclosure.

FIG. 38 is a simplified flowchart illustrating a method of establishinga stimulation treatment protocol for a patient according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Variousfeatures may be arbitrarily drawn to different scales for simplicity andclarity.

The human nervous system includes a complex network of neurologicalstructures that extend throughout the body. As shown in FIG. 1, thebrain interconnects with the spinal cord which branches into thebrachial plexus near the shoulders and the lumbar plexus and sacralplexus in the lower back. The limb peripheral nerves of the arms extenddistally from the brachial plexus down each arm. Similarly, the limbperipheral nerves of the legs extend distally from the lumbar plexus andsacral plexus. A number of the larger limb peripheral nerves areidentified in FIG. 1. As discussed further below, certain aspects of thepresent invention are particularly well suited to stimulation of limbperipheral nerves, including those identified in FIG. 1.

FIG. 2 illustrates a simplified block diagram of a medical system 20 toprovide an example context of the various aspects of the presentdisclosure. The medical system 20 includes an implantable medical device30, an external charger 40, a patient programmer 50, and a clinicianprogrammer 60. The implantable medical device 30 can be implanted in apatient's body tissue. The implantable medical device 30 may include animplantable pulse generator (IPG) 70. In some embodiments, the IPG 70 isa peripheral neurostimulator (PNS) device. The IPG 70 is coupled to oneend of an implantable lead 75. The other end of the implantable lead 75includes multiple electrode surfaces 80 through which electrical currentis applied to a desired part of a body tissue of a patient. Theimplantable lead 75 incorporates electrical conductors to provide a pathfor that current to travel to the body tissue from the IPG 70. Althoughonly one implanted lead 75 is shown in FIG. 1, it is understood that aplurality of implanted leads may be attached to the IPG 70. Furthermore,the type of implanted lead that may be used in the medical system 20 isnot limited to the embodiment shown in FIG. 1. For example, a paddlelead may be implemented in certain embodiments.

The external charger 40 of the medical device system 20 provideselectrical power to the IPG 70. The electrical power may be deliveredthrough a charging coil 90. In some embodiments, the charging coil canalso be an internal component of the external charger 40. The IPG 70 mayalso incorporate power-storage components such as a battery or capacitorso that it may be powered independently of the external charger 40 for aperiod of time, for example from a day to a month, or longer, dependingon the power requirements of the therapeutic electrical stimulationdelivered by the IPG.

The patient programmer 50 and the clinician programmer 60 may beportable handheld devices that can be used to configure the IPG 70 sothat the IPG 70 can operate in a certain way. The patient programmer 50is used by the patient in whom the IPG 70 is implanted. The patient mayadjust the parameters of the stimulation, such as by selecting aprogram, changing its amplitude, frequency, and other parameters, and byturning stimulation on and off. The clinician programmer 60 is used by amedical personnel to configure the other system components and to adjuststimulation parameters that the patient is not permitted to control,such as by setting up stimulation programs among which the patient maychoose, selecting the active set of electrode surfaces in a givenprogram, and by setting upper and lower limits for the patient'sadjustments of amplitude, frequency, and other parameters. It is alsounderstood that although FIG. 2 illustrates the patient programmer 50and the clinician programmer 60 as two separate devices, they may beintegrated into a single programmer in some embodiments.

FIGS. 3A-3B illustrate various example regions of the human body withinwhich a peripheral PNS device may be implanted. For example, referringto FIG. 3A, a lower leg 100 of a patient is illustrated. As anembodiment of the implantable medical device 30 discussed above withreference to FIG. 2, a PNS device 105 is implanted in the lower leg 100,for example, near the calf muscles. Through an elongate lead body 110,the PNS device 105 is electrically coupled to implanted electrodes 112.The electrodes are positioned for stimulation of the posterior tibialnerve 115. In the illustrated embodiment, the PNS device 105, the leadbody 110, and the implanted electrodes 112 all reside below the knee andare contained within the length of the tibia 122 and the fibula 124. Inother words, the lead body 110 does not traverse a joint as it extendsbetween the PNS device 105 and the implanted electrode 112. In theillustrated embodiment, the PNS device 105, the lead body 110, and theimplanted electrodes 112 are positioned between a knee joint and anankle joint.

Referring now to FIG. 3B, another example PNS device 150 is implantedalong the humerous bone. The PNS device 150 is coupled to implantedelectrodes 154 through a lead body 152. The PNS device, the lead body152, and the implanted electrodes 154 are positioned along the humerousbone without extending into or across the adjacent joints in theshoulder or elbow. Similarly, another example PNS device 160 may beimplanted along and within the length of the radius and ulna bones. ThePNS device 160 is coupled to implanted electrodes 164 through a leadbody 162. The PNS device 160, the lead body 162, and the implantedelectrodes 164 are implanted under the skin of the forearm but withoutany of the components extending into the adjacent joints of the elbowand the wrist. As yet another example, a PNS device 180 may be implantedalong a metacarpus bone in the hand. The PNS device 180 is coupled toimplanted electrodes 184 through a lead body 182. The implantation ofthe PNS device 180, the lead body 182, and the implanted electrodes 184is configured such that none of them extends across an adjacent joint inthe wrist or the fingers.

It is understood that FIGS. 3A-3B merely illustrate several examplesites of the body in which a PNS device may be implanted to stimulateone or more target nerves (such as the posterior tibial nerve in FIG.3A). A PNS device may also be implanted in a number of other differentperipheral nerves locations shown in FIG. 1. For instance, a PNS devicemay be implanted in a patient's arms to stimulate one or more of themedian, ulnar, radial, and brachial plexus nerves, as well as in apatient's legs to stimulate one or more of the tibial, saphenous,sciatic, and femoral nerves. For reasons of simplicity, theseconfigurations are not specifically illustrated herein.

Referring now to FIGS. 4-5, a PNS device 200 is illustrated according toan embodiment of the present disclosure. In general, peripheral nervestimulation is a technique configured to provide medical therapy fordifferent diseases and/or to treat different types of pain. Dependingupon the therapeutic application, peripheral nerve stimulation systemsgenerally seek to activate only motor nerves (e.g., for functionalpurposes, such as dorsiflexion for a dropped foot, or a grasp for upperextremity hemiplegia) or only sensory nerves (e.g., for neuropathic painmanagement).

In treating pain, stimulation of innocuous sensory fibers in theperiphery ostensibly affects pain transmission to the brain via the GateControl Theory. Clinically, stimulation of these fibers usually resultsin a comfortable, moderate ‘buzzing’ sensation in the area of pain,termed paresthesia.

In general, peripheral nerve stimulation can utilize relatively simplestimulation techniques to provide excellent therapy. However, PNStherapy today is generally delivered by equipment designed for spinalcord stimulation (SCS). Spinal cord stimulation equipment utilizes largeand overpowered implantable pulse generators (IPGs) designed not forstimulating peripheral nerves, but is designed to deliver electricalpulses to the spinal column. IPGs designed for SCS is also placed inlarge pockets in the lower back/upper buttock, rather than beingimplanted near the targeted peripheral nerve for electrical stimulation.These poorly adapted technologies for peripheral nerve therapy can causesignificant tissue morbidity in the need to route the wires between thetargeted peripheral nerve and the distantly located IPG unit. This, inturn, can result in frequent device failure (and thus therapy failure)due largely to lead migration and breakage. In many cases where SCSequipment was used for PNS, a large percentage of patients neededrevision surgeries to address issues with the SCS IPG and leads.Additionally, while some peripheral nerve pain can be addressed bystimulating the nerve root through SCS of the spinal column, it can bedifficult to achieve effective pain relief with respect to a targetednerve and anatomy without affecting nearby, undesired areas.

To overcome the limitations associated with using SCS equipment toperform PNS, the present disclosure provides a small, flexible PNSsystem—an example embodiment of which includes the PNS device 200 shownin FIGS. 4-5—that can be made simple and small enough to be deployed ina minimally invasive surgical procedure, locally to the region of thetargeted nerves, thereby avoiding tunneling through tissue to remoteregions of the anatomy.

In some embodiments, the PNS system is characterized by a low partscount, low cost-of-goods, ease of manufacturability, a high energydensity long lasting rechargeable battery, use of known biocompatiblematerials, compatibility with industry preferred electrode/lead systems,and a hermetic implantable device geometry that is well suited for mostpreferred anatomical locations. In some embodiments, the system,although simplified, is still flexible enough to handle a wide range ofunilateral and bilateral applications, has high stimulation power outputcapability, covers accepted ranges of therapeutic waveform frequency andduration, can drive multiple leads of eight or more contacts each, andutilizes custom software applications reconfigurable for the differentclinical applications (e.g., pain, incontinence, depression, epilepsy,etc.).

In some embodiments, the PNS system of the present disclosure includesthe PNS device 200 in the form of a hermetically-sealed implantablepulse generator. The PNS device 200 has a miniature form factor. Forexample, the PNS device 200 may have a total volume of less than 5 cubiccentimeters and a thickness less than 5 millimeters. To illustrate thesmall dimensions of the PNS device 200, FIG. 5 shows the PNS device 200next to a quarter. As can be seen in FIG. 5, the PNS device 200 isshorter than the quarter and not much longer either. Such small packagesize of the PNS device 200 enables comfortable and cosmeticallyattractive placement of the PNS device 200 on the limbs of the patient.

Furthermore, the PNS device 200 offers one or more of the followingfeatures:

-   -   Active can/enclosure technology that allows for broader        stimulation fields;    -   Deep drawn small but shallow rectangular form factor for the can        that allows for ease of manufacture and low cost;    -   Connects to proximal ends of “industry standard” electrodes,        which have become preferred for ease of handling        characteristics;    -   Single piece high reliability connector stack;    -   High density pin-less hermetic feedthrough connection system;    -   Two reversibly connectible header ports enable connection of two        leads for multi-region stimulation targeting, nominally distal        from implanted package;    -   High number of contacts per lead to allow for a wide range of        lead designs (for instance, 8 tightly spaced contacts per lead)        and different therapeutic applications (for instance, chronic        intractable pain).

In addition to the PNS device 200, the PNS system of the presentdisclosure may also include an external stimulator used for trialtherapy periods, one or more leads with corresponding electrodes, anextension for a lead/electrode, accessories such as lead anchors andsurgical procedure tools, a remote control and pulse generator chargerthat may be combined into one device, and/or a remote controller forphysician or patient programming use.

For example, FIGS. 6A-6C illustrate an example electronic programmer 250configured to send programming instructions to the PNS device 200. ThePNS device 200 generates a corresponding electrical stimulation therapy(e.g., a series of electrical stimulation pulses) in response to thereceived programming instructions. In certain embodiment, the electronicprogrammer 250 is configured to be used by either the patient or ahealthcare professional. As such, the electronic programmer 250 may beviewed as an embodiment of the patient programmer 50 and the clinicianprogrammer 60 integrated together as a single device.

As is shown in FIG. 6A, the electronic programmer 250 has a“smartphone-like” industrial design. For example, the electronicprogrammer 250 has a touchscreen (e.g., a capacitive touchscreen)graphical user interface with virtual buttons and input/output fields.The electronic programmer 250 may also have tactile buttons that providean immediate control input to the programmer 250 for quick and simplecore system functions. Such “smartphone-like” design reduces the stigmaof using a medical device. The “smartphone-like” design of theelectronic programmer also makes it easier for the user of theelectronic programmer to learn how to use it quickly, since smartphoneshave become very popular, and most people are comfortable interactingwith a smartphone-like user interface.

Aside from its elegant and intuitive industrial design, the electronicprogrammer 250 also offers flexible functionalities. For example, theelectronic programmer 250 may be configurable from patient to patient,according to the patient's level of technical competence and/or comfort.The electronic programmer 250 may also be reconfigurable via firmwarefor different therapeutic applications (for instance, chronicintractable pain). Furthermore, the electronic programmer 250 may havemultiple user modes: e.g., patient programming and patient charging mode(both configurable by a clinician), clinician mode, engineering mode,diagnostic mode, etc.

Referring to FIG. 6B, the electronic programmer 250 also includes anonboard battery 260. In the illustrated embodiment, the battery 260 issealed within the housing of the electronic programmer 250 and isnon-removable. In alternative embodiments, however, the battery 260 maybe user-removable. The battery 260 is a rechargeable battery. In variousembodiments, the battery 260 has a capacity ranging from about 400milli-amp hours (mAh) to about 4000 mAh, for example with a capacityaround 2700 mAh. The rechargeable nature of the battery 260 allows it tohave a reduced size and mass.

The electronic programmer 250 also has a USB port 265, which allows theelectronic interchange (e.g., telemetry or power) between the electronicprogrammer 250 and external devices. For example, referring to FIG. 6C,a charger 270 is coupled to the USB port 265 of the electronicprogrammer 250 through a USB cable 280. The battery 260 may providepower to the charger 270, which contains internal charging electronicsand a charge coil for inductively charging the PNS device 200 discussedabove. This type of power/charging configuration shown in FIGS. 6B-6Cgreatly simplifies patient tasks with respect to charging the PNS device200, as patients only has a few things to manage. In addition, chargingcan be done at any time as needed and while the patient isambulatory/mobile.

The electronic programmer 250 and the charger 270 are also bothimplemented in small and lightweight packages. For example, they mayeach have a thickness less than about 10 millimeters (mm) The small sizeof the electronic programmer 250 and the charger 270 enablescomfortable, convenient, and cosmetically attractive wearing of theelectronic programmer 250 and/or the charger 270 on a patient's limb,for example with a detachable belt or band. In some embodiments, therelative simplicity and versatility of the electronic programmer 250discussed above reduce or eliminate the need for a cumbersome separateclinician programmer.

The various sections and components of the PNS device 200 will now bediscussed in more detail below.

Referring to FIG. 7, a simplified block diagram of the PNS device 200 isillustrated. The PNS device 200 includes a power supply circuitrysection 300, a stimulation circuitry section 305, and a telemetrycircuitry section 310. The power supply circuitry section 300 includesan inductive charging component 320. In some embodiments, the chargingcomponent 320 includes a coil for receiving power/energy inductivelyfrom an external charger, for example from the charger 270 discussedabove with reference to FIG. 6C. In some embodiments, the inductiveenergy (i.e., the charging signal) received from the inductive chargingcomponent 320 ranges from about 0.1 volts to about 5 volts in amplitude,and it has a frequency range that is within one of the Industrial,Scientific, and Medical (ISM) radio bands. For example, in someembodiments, the inductive energy is in a 13.56 Mhz band, that is, itranges from 13.553 Mhz to 13.567 Mhz with a center frequency at 13.56Mhz. In other embodiments, the inductive energy may be in alternativeISM radio bands.

The power supply circuitry section 300 further includes a circuitnetwork 325. The circuit network includes microelectronic componentsthat provide a resonant frequency at or near the center frequency of theISM radio band associated with the inductive energy received by thecharging component 320. Thus, in the embodiments where the inductiveenergy is in the 13.56 Mhz ISM radio band, the microelectroniccomponents of the circuit network 325 provide a resonant frequency at ornear 13.56 Mhz. This resonant frequency allows the inductive energy topass through, but effectively rejects signals from outside the selectedISM radio band. For example, telemetry signals that have much higher (orlower) frequencies than the selected ISM radio band will be blocked bythe circuit network 325. In this manner, the circuit network 325 mayfunction similar to a filter. The various aspects of the circuit network325 will be discussed in greater detail below.

The power supply circuitry section 300 also includes a charging circuit330 that is electrically coupled to the inductive charging component320. The charging circuit 330 includes various electronic componentsthat convert the inductive energy received from the inductive chargingcomponent 320 into a direct current (DC) voltage. In some embodiments,the charging circuit 330 may include a voltage booster that can converta lower input voltage to a higher output voltage, so as to adequatelycharge a battery 340 coupled thereto. In some embodiments, the battery340 is configured to output a DC output voltage ranging from about 3.5volts to about 4 volts. Thus, the charging circuit 330 can boost aninput voltage (e.g., received from the inductive charging component 320)to meet or exceed the requisite DC output voltage of the battery 340.

The power supply circuitry section 300 further includes an energyharvesting component 350 that is configured to supply power to thebattery 340. As is illustrated, the output of the energy harvestingcomponent 350 is electrically coupled to the charging circuit 330, whichboosts the energy harvested by the energy harvesting component to alevel that can be used to charge the battery 340. In some embodiments,the energy harvesting component 350 includes a thermoelectric generator(TEG) that converts the body heat of the patient (inside whom the PNSdevice 200 is implanted) to electrical energy. The converted electricalenergy may then be used to charge the battery 340 (after being boostedup by the charging circuit 330). In some other embodiments, the energyharvesting component 350 may also include circuitry to convert infraredlight and/or vibration and movement of the patient into electricalenergy. In various embodiments, the electrical energy harvested by theenergy harvesting component 350 may exceed about 100 millivolts (mV).

The power supply circuitry section 300 also includes a voltagedown-converter 360 coupled to the battery 340. The voltagedown-converter 360 converts the nominal DC output voltage of the battery340 to a lower level suitable for powering some of the electroniccircuitry of the PNS device 200, such as a microcontroller, amplifiers,and telemetry circuitry (discussed below in more detail). For example,in embodiments where the DC voltage output of the battery 340 is about 4volts, the down-converter 360 reduces it to about 2.7 volts. In theillustrated embodiment, 2.7 volts is a sufficient voltage to powerelectronic components such as the microcontroller, amplifiers, or thetelemetry circuitry, and thus there is no need to waste the highervoltage output (e.g., 4 V) produced by the battery 340. In other words,the voltage down-converter 360 saves energy by down-converting the DCvoltage output of the battery 340. In some embodiments, the voltagedown-converter 360 includes a buck regulator or a low-dropout (LDO)linear regulator.

The power supply circuitry section 300 further includes a voltageup-converter 370 coupled to the battery 340. The voltage down-converter370, when turned on, converts the nominal DC output voltage of thebattery 340 to a higher level to enable high output voltage compliancefor electrical stimulation. In more detail, the electrical stimulationpulses for the stimulation therapy may require higher voltages (e.g., ashigh as 12 volts) than the nominal DC voltage output of the battery 340.In these cases, the voltage up-converter 370 may be activated to boostthe DC output voltage of the battery 340, for example from 4 volts to 8volts or 12 volts, or at a fractional value in between. In theillustrated embodiment, the voltage up-converter 370 supplies power tostimulation circuitry (e.g., stimulation driver) that will be discussedbelow in more detail. To accomplish the voltage boost, the voltageup-converter 370 includes a charge pump in the present embodiment, butit is understood that it may include alternative types of voltageup-converters in alternative embodiments.

It is understood that the specific voltage values here are providedmerely as an example and are not intended to be limiting. For example,the voltage down-converter 360 may down-convert a 4 volt DC output ofthe battery 340 to a 2.3 volt DC voltage that will then be supplied tocertain electronic circuitry of the PNS device 200. As another example,the voltage up-converter 370 may up-convert a 4 volt DC output of thebattery 340 to a number that is a fraction (greater than 1) of the 4volt DC voltage.

The stimulation circuitry section 305 includes a microprocessor ormicrocontroller 400 (referred to as a microcontroller hereinafter) thatis powered by the output of the voltage down-converter 360. Themicrocontroller 400 controls various operations of the PNS device 200.For example, the microcontroller 400 is configured to generateelectrical stimulation pulses in response to programming instructionsreceived from a programmer, such as from the electronic programmer 250discussed above with reference to FIGS. 6A-6C. In various embodiments,the microcontroller 400 may include a microcontroller chip (e.g., anapplications processor) with internal instruction and data caches,multimedia capabilities, external memory interfacing, and interfacingflexibility.

The microcontroller 400 may also include memory such as FLASH memory, aread-only memory (“ROM”), a random access memory (“RAM”), anelectrically erasable programmable read-only memory (“EEPROM”), a harddisk, an optical disk, or another suitable magnetic, optical, physical,or electronic memory device. In some embodiments, the microcontroller400 includes a double data rate (DDR2) synchronous dynamic random accessmemory (SDRAM) for storing data relating to and captured during theoperation of the portable electronic device 90. Of course, other typesof data storage devices may be used in place of the data storage devicesdiscussed herein. It is understood that the different types of memorydiscussed above may be integrated into the microcontroller chipdiscussed above or may be separately implemented from themicrocontroller chip. Software code, firmware code, or other types ofprogram modules and applications may be stored on the memory and may beexecuted to perform certain tasks, such as generating the stimulationpulses.

According to some embodiments, the microcontroller 400 is configured toperform one or more of the following tasks:

-   -   Generate stimulation waveforms with internal 12-bit DAC, contact        combinations, and manages compliance voltage    -   Manage bidirectional telemetry & external communications    -   Manage sensing for impedance, battery voltage, and physiological        signals    -   Store data for diagnostics and device use tracking    -   Store Code, bootloader, and other suitable data in onboard FLASH        and RAM    -   Enter various power-conservation consumptions modes to reduce        power consumption    -   Manages emergency ON/OFF states from a magnetic switch    -   Reconfigure system with a new firmware download

As is shown in FIG. 7, the microcontroller 400 includes amicrocontroller core 410. Most of the functions of the microcontroller400 discussed above may be performed by, or at least in part by, themicrocontroller core 410. As such, the microcontroller core 410 is apower-hungry device and consumes significantly more power than the restof the components of the microcontroller 400. In order to save power,the microcontroller 400 also includes a direct memory access (DMA) unit420. In some embodiments, the DMA unit 420 is a task handler that canoperate independently from the microcontroller core 410. For example,the DMA unit 420 may be capable of sending instructions to peripherals(discussed in more detail below) within the microcontroller 400, withouthaving to go through the microcontroller core 410. One benefit of usingthe DMA unit 420 is that it consumes substantially less power than themicrocontroller core 410. For example, in some embodiments, the DMA unit420 consumes less than 10% of the power of the microcontroller core 410.Therefore, according to various aspects of the present disclosure, theDMA unit 420 may be utilized to execute certain simple tasks while themicrocontroller core 410 is turned off in order to reduce powerconsumption.

The microcontroller 400 further includes a plurality of peripherals,channels, or buses. For example, the microcontroller 400 may include adigital-to-analog converter (DAC) to generate the waveforms for theelectrical stimulation pulses. The microcontroller 400 may also includean analog-to-digital converter (ADC) to convert an analog feedbacksignal to digital numbers. The microcontroller 400 may also include aVBOOST_EN line that is electrically coupled to the voltage up-converter370. When the VBOOST_EN line is enabled, the voltage up-converter 370 isactivated and doubles or triples the DC output voltage from the battery340, or scales up the DC output voltage from the battery 340 by afractional number greater than 1. In some embodiments, the VBOOST_ENline is only enabled to turn on the voltage up-converter 370 during thestimulation pulse. Between consecutive stimulation pulses, the VBOOST_ENline is disabled to turn off the voltage up-converter 370. In thismanner, power consumption is reduced, since the voltage up-converter isnot running all the time. The microcontroller 400 further includes anInput/Output (I/O) bus, a Serial-Peripheral-Interface (SPI)communication bus, and an Inter-Integrated-Circuit (I²C) communicationbus, which allow the microcontroller 400 to communicate with peripheralsor external devices.

Another peripheral-like device of the microcontroller 400 is a timerunit 425. The timer unit 425 includes hardware and firmware/softwarethat control the timing for turning on and off the microcontroller core410 and/or enabling/disabling the peripherals or other components of thePNS device 200. Although not illustrated herein for reasons ofsimplicity, the microcontroller 400 may also include one or moreinternal clocks. These internal clocks serve as timing sources for thetimer unit 425.

In addition, a crystal oscillator 430 is external to the microcontroller400 and is coupled to the microcontroller 400. In some embodiments, thecrystal oscillator 430 generates a 32.678 Khz clock that may be usedwhen the microcontroller 400 enters a power-conservation operating mode(also referred to as a low-power mode or a sleep mode) to reduce powerconsumption. The crystal oscillator 430 may also serve as a timingsource for the timer unit 425.

In addition to the microcontroller 400, the stimulation circuitry 305further includes a plurality of sensors that are electrically orcommunicatively coupled to the microcontroller 400. In the illustratedembodiment shown in FIG. 7, a magnetic sensor 435 is coupled to themicrocontroller 400 through the I/O bus, and a temperature sensor 440and an accelerometer 445 are each coupled to the microcontroller 400through the I²C communication bus. In some embodiments, the magneticsensor 435 may be used to turn on or off the PNS device 200, thetemperature sensor 440 may be used to facilitate the energy harvested bythe energy harvesting component 350, and the accelerometer 445 may beused to detect a posture of the patient, which may then be used toperform posture-dependent calibration. It is understood that thesesensors 435-445 are merely examples, and that additional sensors such aspressure sensors, humidity sensors, vibration sensors, proximitysensors, light sensors, strain/stress sensors, transducers, gyroscopes,or compasses may be implemented in the PNS device 200 in variousembodiments.

The stimulation circuitry section 305 further includes a stimulationdriver 450 coupled to the DAC output of the microcontroller 400. Thestimulation driver 450 includes amplification circuitry (e.g., op-amps)that is capable of amplifying an amplitude of the stimulation pulsesgenerated by the DAC of the microcontroller 400. For example, in someembodiments, the stimulation driver 450 can amplify the amplitude of thestimulation pulses by a factor of 5. The amplification (or scaling up)of the variation stimulation waveforms (i.e., the stimulation pulsesoutputted by the DAC) obviates the need for a custom DAC.

The stimulation circuitry section 305 also includes stimulationmultiplexers 460 that are coupled to the stimulation driver 450. Themultiplexed stimulation outputs allow for configured stimulation contactcombinations. In more detail, the stimulation multiplexers 460 serve asan array (e.g., 16 for anodes and 16 for cathodes) of switches thatcoupled to a plurality of stimulation channels through DC-blockingcapacitors 465, respectively. The switches are coupled in parallel toone another. Through the turning on and off of these switches,electrical stimulation pulses can be delivered to the desiredstimulation channel(s).

To help conserve energy, the stimulation driver 450 and the stimulationmultiplexers are powered by either the battery 340 directly, or by thevoltage output produced by the voltage up-converter 370, but not both.For example, when the stimulation pulse amplitude is less than what thebattery 340 is capable of providing (e.g., stimulation voltage is at 3volts, and the battery 340 outputs 4 volts), the voltage up-converter370 need not be turned on, because the voltage up-converter 370 wouldconsume power when it is turned on. The voltage up-converter 370 isturned on when the stimulation pulse demands a greater amplitude thanthe battery 340 is capable of providing. In this manner, the voltageup-converter 370 is selectively turned on or off to minimize powerconsumption. Thus, the output of the voltage up-converter 370 serves asthe power supply for the stimulation driver 450 and the stimulationmultiplexers 460 when needed, and the battery 340 serves as the powersupply the rest of the time.

To ensure such operation, the present disclosure implements a diode 470coupled between the output of the battery 340 and the inputs of thestimulation driver 450 and the stimulation multiplexers 460. Anotherdiode 475 is also implemented between the output of the voltageup-converter 370 and the inputs of the stimulation driver 450 and thestimulation multiplexer 460. These two diodes 470 and 475 are coupled inparallel with each other and serve as switches such that only one pathis created between the power source (either the battery 340 or thevoltage up-converter 370) and the stimulation driver 450 and thestimulation multiplexer 460. When the voltage up-converter 370 is turnedon, the diode 475 is forward-biased to create a charging path from thevoltage up-converter 370 and the stimulation driver 450 and thestimulation multiplexers 460, while the diode 470 is reverse-biased toblock the path from the battery 340 to the stimulation driver 450 andthe stimulation multiplexers 460. This also ensures that the voltageup-converter 370 will not inadvertently charge the battery 340. When thevoltage up-converter 370 is turned off, the diode 470 is forward-biasedto create a charging path from the battery 340 and the stimulationdriver 450 and the stimulation multiplexers 460, while the diode 475 isreverse-biased to block the path from the voltage up-converter 370 tothe stimulation driver 450 and the stimulation multiplexers 460.

The stimulation circuitry section 305 further includes a switch 480 thatis coupled between the output of the voltage up-converter 370 and theinputs of the stimulation driver 450 and the stimulation multiplexers460. The switch 480 is also coupled to the microcontroller 400. Inresponse to instructions from the microcontroller 400, this switch 480may disconnect any load (e.g., the stimulation driver 450 and thestimulation multiplexers 460) from the voltage up-converter 370 betweenconsecutive stimulation pulses, thereby preserving energy stored in thevoltage up-converter 370 for the next stimulation pulse.

The stimulation circuitry section 305 may also include a sense amplifier490 coupled between the output of the stimulation multiplexers and themicrocontroller 400. In certain embodiments, the sense amplifier 490 isconfigured to sense action potentials of a target nerve. The sensedaction potentials are fed back to the microcontroller for furtherprocessing and analysis. In some embodiments, the sense amplifier 490can also measure impedance values.

The telemetry circuitry section 310 includes a telemetry block 500. Thetelemetry block 500 is powered by the voltage down-converter 360. Thetelemetry block 500 is also electrically and communicatively coupled tothe microcontroller 400. The telemetry block 500 includes one or moretransmitters, receivers, and/or transceiver. For example, the telemetryblock 500 may include one or more of the following: a Medical ImplantCommunication Services (MICS) transceiver, an Industrial, Scientific andMedical (ISM) transceiver, a Wi-Fi transceiver, a Bluetooth transceiver,DLNA, or any of the 3G or 4G cellular networking transceivers. Throughthe telemetry block 500, the PNS device 200 may conduct bi-directionaltelecommunications with external devices, for example turning on/off thePNS device 200, receiving commands or programming instructions from theelectronic programmer 250 discussed above, or transfer diagnostic dataor unique patient information to the electronic programmer 250 or to aremote server.

The telemetry circuitry section 310 further includes an antenna 510 fortransmitting and receiving telemetry signals. In some embodiments, theantenna 510 and the inductive charging component 320 may be the samecomponent. In other words, a single conductive component such as a loopcoil or wire may be used to charge the PNS device 200 and to conducttelecommunications with the PNS device 200.

For example, the antenna 510 may receive telemetry signals that are indifferent radio bands, such as signals in a MICS band (between 402 Mhzand 405 Mhz, which may hereinafter be referred to as a 400 Mhz MICSband) and signals in a 2.45 Ghz ISM band (between 2.4 Ghz and 2.5 Ghz).The telemetry signals in the 2.45 Ghz band may be used to “wake up” thePNS device 200, which is normally in a deep “sleep” mode, where littlepower is being consumed. After the PNS device 200 is “woken up,” thetelemetry signals in the MICS band are used to conducttelecommunications between the PNS device 200 and external devices suchas the electronic programmer 250. Since the PNS device 200 employs asingle antenna 510 to receive multiple types of telemetry signals, thesedifferent types of telemetry signals need to be properly discriminated,otherwise one type of telemetry signals may cause interference or createnoise for the other type of telemetry signals.

According to the various aspects of the present disclosure, thetelemetry circuitry section 310 includes a plurality of circuits orcircuit networks to discriminate different types of input signalsreceived from the antenna 510. In the illustrated embodiment, circuitnetworks 520 and 530 are implemented in the telemetry circuitry section310. The circuit network 520 includes microelectronic components thatwill allow the telemetry signals in the MICS radio band to pass throughbut will reject signals outside the MICS radio band, including thetelemetry signals in other bands (e.g., telemetry signals in the 2.45Ghz band) and charging signals (e.g., charging signals in the 13.56 MhzISM band). The circuit network 530 includes microelectronic componentsthat will allow the telemetry signals in the 2.45 Ghz radio band to passthrough but will reject signals outside the 2.45 Ghz radio band,including the telemetry signals in other bands (e.g., telemetry signalsin the 400 Mhz MICS band) and charging signals (e.g., charging signalsin the 13.56 Mhz ISM band). In this manner, the circuit networks 520 and530 provide discrimination for the input signals.

It is understood that although the circuit network 325 is not a part ofthe telemetry circuitry section 310, it also helps providediscrimination of the input signals. As discussed above, the antenna 510and the inductive charging component 320 may be the same conductivecomponent, for example, a single turn wire or coil. In other words, thesame wire or coil may be used to receive both charging signals (e.g.,inductive energy in the 13.56 Mhz ISM band) and telemetry signals in the400 Mhz MICS band and telemetry signals in the 2.45 Ghz band. Thus, thecircuit network 530 includes microelectronic components that will allowthe charging signals in the 13.56 Mhz ISM band to pass through but willreject signals outside the 13.56 Mhz ISM band, including the telemetrysignals in the 400 Mhz MICS band and in the 2.45 Ghz ISM band.

The circuit networks 520 and 530 may also each include passivecomponents such as inductors and capacitors for impedance matching.Impedance matching may maximize power transfer or may reduce signalreflection (for example, reflection from a load). In the illustratedembodiment, the circuit networks 520 may include passive circuitelements collectively arranged to match the impedances of the telemetryblock 500 and the antenna 510 in the 400 Mhz MICS band. In someembodiments, the circuit network 530 may also include passive circuitelements collectively arranged to match the impedances of the telemetryblock 500 and the antenna 510 in the 2.45 Ghz frequency band.

FIGS. 8A-8L are detailed circuit schematics of the PNS device 200according to an embodiment of the present disclosure. However, it isunderstood that the PNS device 200 may be implemented differently inalternative embodiments and is not limited to the specificimplementation shown in FIGS. 8A-8L.

Paddle Lead Maximizing Lateral Target Points Across a Peripheral Nerve

As discussed above, unlike spinal cord stimulation devices, the PNSdevice 200 is specifically configured to deliver electrical stimulationfor peripheral nerves. Referring to FIG. 9, peripheral nerves comprise‘bundles’ (e.g., bundles 570) of groupings of axons called fascicles.Typically, a fascicle innervates a particular area or region of thebody. Additionally, some fascicles carry a predominance of efferentmotor fibers while others carry mostly afferent sensory fibers.

Depending upon the therapeutic application at hand, peripheral nervestimulation systems typically seek to activate only motor nerves (e.g.,for functional purposes, such as dorsiflexion for a dropped foot, or agrasp for upper extremity hemiplegia), or only sensory nerves (e.g., forneuropathic pain management). In any particular application, neuralselectivity is usually achieved by maximally activating the targetedfascicles while avoiding activation of those fascicles that may lead toside effects (e.g., in pain management, stimulation of motor nerves canlimit the efficacy of the therapy that is to be provided).

One method of peripheral nerve stimulation uses paddle leads, asimplified example of which is shown as a lead 580 in FIG. 9. Concertedeffort is required to place paddles at least near or over the targetedfascicles, but this can usually be achieved intraoperatively in anominal amount of time.

One challenge with paddle leads in peripheral nerve stimulation is theneed to provide contacts or electrodes in the paddle lead that are of acertain size or surface area so that charge density concerns can bemanaged, which include avoiding the creation of toxic electrochemicalproducts generated by stimulation currents at the contact or electrodelocation, or associated with contact corrosion. Typical paddleelectrodes or contacts are rectangular with a nominal surface area. Thecontact width necessary to maintain current flow below charge densitylimits is such that the ability to provide fine fascicular targetingbecomes limited, in part because contacts can only be placed on a paddlelead such that they do not electrically short together duringmanufacture or implantation. What is needed includes a paddle leadconfigured to maximize transverse fascicular targeting or selectivity ina peripheral nerve, or a paddle lead that permits fine separation offascicles in a targeted nerve.

Referring now to FIG. 10, a simplified diagrammatic view of an exampleimplantable lead 600A of the present disclosure is illustrated accordingto an embodiment. The implantable lead is configured to be coupled orattached to the PNS device 200 discussed above. The implantable lead600A delivers electrical stimulation pulses generated by the stimulationcircuitry 305 of the PNS device 200 to target peripheral nerves. Theimplantable lead 600A includes an elongate flexible/bendable lead body610 that includes a coupling assembly (not specifically illustratedherein), which is configured to be coupled to the PNS device 200. Theimplantable lead 600A also includes a paddle 620A that includes aplurality of electrodes (also referred to as contacts), for exampleelectrodes 1-8 as shown in FIG. 10. Electrical stimulation pulses aredelivered to the target peripheral nerve through these electrodes.

According to various aspects of the present disclosure, the electrodes1-8 are collectively arranged in a manner such that they provide aplurality of unique centerlines 631-638. For example, the paddle lead600A includes a plurality of rows of electrodes oriented along itslength such that the respective centerline of the electrode(s) on eachrow is mostly or completely different from those on other rows. In theillustrated embodiment, the centerlines 631-638 extend in an X-directionor along an X-axis, whereas the fascicles of the target peripheral nervetypically extend in a Y-direction or along a Y-axis (perpendicular tothe X-axis). In general, it is desired to try to keep the centerlines ofthe electrodes in the middle of the targeted nerves, as it offersredundancy and flexibility to recover/restore stimulation inspite ofslight movements of the nerve or electrode.

Most conventional paddle leads typically employ a grid approach for itselectrodes, where the electrodes are neatly arranged into rows andcolumns, and where all the electrodes in the same row are aligned withone another (e.g., aligned along the X-axis), and all the electrodes inthe same column are aligned with one another (e.g., aligned along theY-axis). Consequently, conventional paddle leads can only offer a verylimited number of unique centerlines. For example, a conventional paddlelead with 9 electrodes with a 3×3 configuration can only offer 3 uniquecenterlines. As discussed above, the centerlines are correlated with theassociated electrode's ability to provide target stimulation. Thus,having a limited number of centerlines may prevent the PNS device fromproviding flexible stimulation therapies.

In comparison, the paddle 620A has a 3-2-3, 8-contact or electrodeconfiguration in the embodiment illustrated in FIG. 10. As is shown inFIG. 10, the 8 electrodes are arranged to achieve 7 unique centerlines(electrodes 2 and 7 have substantially the same centerline) transverselydisposed across the nerve over which it is placed. In other words, asubstantial majority (7 out of 8) of the electrodes on the paddle 620Ahave their own respective unique centerlines. Alternatively stated, theelectrodes 1-8 on the paddle 620 are “staggered.” Such staggered 3-2-3electrode arrangement of the paddle lead 600A permits fine separationsof fascicles (or allows for greater fascicular selectivity) in a nerveto be targeted, because individual electrodes can be activated ascathodes on different rows to ‘sweep’ the stimulation field across thenerve to find the location that maximizes the desired therapeutic effectwhile minimizing side effects. In some embodiments, the electrodes631-638 of the paddle lead 600A are configured to take into account thetendency of fascicles in peripheral nerves to run in a relatively fixedlongitudinal course along the length of the nerve that is to bestimulated.

In addition, since the paddle lead 600A is configured for peripheralneural stimulation, the spacing between adjacent electrodes may be smalltoo. In some embodiments, a distance 650 separating adjacent electrodesin the X-direction is in a range from about 1 millimeters (mm) to about5 mm, and a distance 655 separating adjacent electrodes in theY-direction is in a range from about 2 millimeters (mm) to about 5 mm.The distance 650 may also be referred to as a horizontal spacing, andthe distance 655 may also be referred to as a vertical spacing.

These distances 650-655 are significantly smaller than the distancesseparating adjacent electrodes on a paddle lead configured to deliverspinal cord stimulation. This is because in the context of spinal cordstimulation, the paddle would be implanted near the spinal cord, whichmay span a great distance. Thus, the paddle lead for spinal cordstimulation is typically configured to have electrodes that are spacedfarther apart, so that they can span a relatively long distance that maybe required to reach the target stimulation site. It is not as importantto achieve such fine resolution in the spinal cord stimulation context.

In comparison, peripheral nerve stimulation is typically focused in arelatively small area. In addition, as discussed above, peripheral nervestimulators need to achieve high neural selectivity in the target nervesuch that only the desired nerve fibers (for example, only the efferentfibers or only the afferent fibers) are activated but not the other. Assuch, peripheral nerve stimulators need to have smaller distancesseparating adjacent electrodes to allow for the high neural selectivity.

It is understood that the electrodes 631-638 may be substantially evenlyor uniformly spaced apart in either the X-direction or the Y-direction(or both) in some embodiments, or they may be unevenly spaced apart inthe X or Y-directions in other embodiments.

FIG. 11 illustrates a simplified diagrammatic view of an implantablelead 600B according to another embodiment of the present disclosure. Theimplantable 600B has a paddle 620B that is similar to the paddle 620Ashown in FIG. 10. However, the electrodes 1-8 of the paddle 620B arearranged such that every electrode has a unique respective centerlinethat extends in the X-direction. In other words, the paddle 620Bachieves a total of 8 unique centerlines with 8 electrodes, compared tothe 7 centerlines achieved by the paddle 620A in FIG. 10.

In some embodiments, electrodes are not arranged in a grid per se, butare offset from one row to the next. In some embodiments, none of theelectrodes in a single row on the paddle are arranged in a singlecolumn. For example, referring now to FIG. 12, a simplified diagrammaticview of an implantable lead 600C is illustrated according to anotherembodiment of the present disclosure. The implantable 600C has a paddle620C that contains electrodes 1-9. The electrodes 1-9 are arranged in astaggered manner in both the X-direction and the Y-direction. In moredetail, the electrodes 1-9 are roughly arranged into 3 “columns” 660,661, and 662, and 3 “rows” 665, 666, and 667. The column 660 includeselectrodes 1-3, the column 661 includes electrodes 4-6, and the column662 includes electrodes 7-9. The row 665 includes electrodes 1, 4, and7, the row 666 includes electrodes 2, 5, and 8, and the row 667 includeselectrodes 3, 6, and 9.

However, the electrodes in each column are not aligned in theY-direction, and the electrodes in each row are not aligned in theX-direction. Rather, the electrodes in each column are still offset fromone another, as are the electrodes in each row. For example, the columns660-662 may each extend in a direction 668 that is somewhat “vertical”but is not parallel to the X-axis or the Y-axis. In other words, thedirection 668 has a greater Y-component than an X-component. The rows665-667 may each extend in a direction 669 that is somewhat “horizontal”but is also not parallel to the X-axis or the Y-axis. In other words,the direction 669 has a greater X-component than a Y-component.

Since the directions in which the columns and rows extend are notparallel with the X or Y axes, the electrodes 1-9 offer unique verticaland horizontal centerlines. According to the embodiment of the paddle620C shown in FIG. 12, the electrodes 1-9 have horizontal centerlines(i.e., centerlines spanning in the X-direction) 631-639, and theelectrodes 1-9 have vertical centerlines (i.e., centerlines spanning inthe Y-direction) 671-679. The electrodes 1-9 are staggered horizontallyand vertically such that they collectively offer 9 unique horizontalcenterlines 631-639, as well as 9 unique vertical centerlines 671-679.

As discussed above, having the plurality of unique horizontal andvertical centerlines 631-639 and 671-679 affords the paddle 620C theflexibility and versatility to selectively stimulate one or more targetnerve fibers but not the undesired nerve fibers, even if the desired andundesired nerve fibers are closely located to one another. In otherwords, the staggered electrode arrangement discussed herein can achievehigh neural selectivity, and the PNS system with the implantable lead600C permits very precise spatial targeting of different portions of anerve.

FIG. 13 illustrates a simplified diagrammatic view of an implantablelead 600D according to yet another embodiment of the present disclosure.The implantable lead 600D is similar to the implantable lead 600C shownin FIG. 12 in that it also offers an electrode arrangement that is bothhorizontally staggered and vertically staggered. However, the electrodes1-9 on the paddle 620D are even more staggered. For example, thehorizontal and vertical distances separating adjacent electrodes may beuneven or non-uniform. As another example, there may not be any lineardirection in which any of the “columns” 660-662 or the “rows” 665-667extend, let alone a direction that is parallel to either the X-axis orthe Y-axis. In some embodiments, even if some of the “columns” or “rows”extend along a particular linear direction, such linear direction wouldnot be parallel with any linear direction of any other “column” or“row.” Stated differently, none of the “columns” 660-662 is parallelwith any other of the columns on the paddle 620D, and none of the “rows”665-667 is parallel with any other of the rows on the paddle 620D. Thehorizontal centerlines 631-639 are still each unique, as are thevertical centerlines 670-679. Again, such staggered electrodearrangement may permit good neural selectivity.

FIG. 14 illustrates a simplified diagrammatic view of an implantablelead 600E according to yet another embodiment of the present disclosure.Here, the implantable lead 600E includes a paddle 620E that has 12electrodes implemented thereon. The 12 electrodes are collectivelyarranged in roughly 3 “columns” and 4 “rows” and collectively define astimulation region 680 on the paddle 620E. The boundaries or outlines ofstimulation region 680 may be defined by a topmost edge of a topmostelectrode (electrode 1 in this case), a bottommost edge of a bottommostelectrode (electrode 12 in this case), a leftmost edge of a leftmostelectrode (electrode 4 in this case), and a rightmost edge of arightmost electrode (electrode 9 in this case). As such, the stimulationregion 680 has approximately a rectangular shape. However, it isunderstood that the outlines or boundaries of the stimulation region 680may not be actually visible on the paddle 620E.

The electrodes 1-12 are staggered to the extent such that no horizontallinear paths (or a straight line parallel to the X-axis) or verticallinear paths (or a straight line parallel to the Y-axis) across thestimulation region 680 may exist without intersecting at least one ofthe electrodes 1-12. Stated differently, within the stimulation region680, every horizontal linear path and every vertical linear path willintersect at least one of the electrodes 1-12. This is due to thepartial overlap in both the X-and-Y-directions among the electrodes1-12. For example, electrodes 1 and 5 are overlapped in the Y-direction,as are electrodes 5 and 9, as are electrodes 9 and 2, as are electrodes2 and 6, so on and so forth. Similarly, electrodes 4 and 3 areoverlapped in the X-direction, as are electrodes 3 and 2, as areelectrodes 2 and 1, as are electrodes 1 and 8, so on and so forth.Therefore, if a horizontal or vertical linear path is to extend acrossthe entire stimulation region 680, one or more of the electrodes 1-12will necessarily be in its path. It may be said that the staggeredelectrode arrangement of the paddle 620E completely blocks allhorizontal and linear paths across the stimulation region 680. As such,the staggered electrode arrangement of the paddle 680 may theoreticallypermit electrical stimulation in almost every target nerve site coveredby the stimulation region 680, thereby imparting a high degree ofadjustability and targetability of delivered electrical stimulus.

It is understood that in some embodiments, such as the embodiment of thepaddle 620C shown in FIG. 12, there may be some horizontal or verticallinear paths that may extend across the entire stimulation region 680without intersecting at least one of the electrodes. However, even insuch embodiments, a substantial majority (e.g., greater than 70%, 80%,or 90% in various implementations) of the available horizontal andvertical linear paths may still intersect with at least one electrode,because there is still some amount of horizontal or vertical overlapamong the electrodes 1-9 on the paddle 620C. Therefore, it may be saidthat in these embodiments (e.g., embodiment shown in FIG. 12), thestaggered electrode arrangement blocks a substantial majority of thehorizontal and linear paths across the stimulation region. Even in theseembodiments, however, the amount of overlap (in the X or Y directions)among the electrodes may still offer a high degree of adjustability andtargetability of delivered electrical stimulus.

In each of the embodiments of the paddle lead 600 shown in FIGS. 10-14and discussed above, there are at least 3 “rows” and/or 3 “columns” ofelectrodes. In other embodiments, any other number of columns or rowsgreater than 3 may be implemented for the paddle with staggeredelectrodes. The greater number of rows or columns allows the paddle tobe better suited for peripheral nerve stimulation, as the peripheralnerves may have irregular shapes and may span in various directions. Incomparison, many conventional paddle leads only have 1 or 2 columns ofelectrodes. This is adequate for spinal cord stimulation, since thetarget nerves in the SCS context extend along the spine, which is mostlystraight and narrow. However, these SCS paddle leads with 1 or 2 columnsof electrodes will not work very well in the peripheral nervestimulation context, since the 1 or 2 columns of electrodes may not beable to reach all the target stimulation areas, and maintain targetedstimulation over desired regions, due to the geometric differencesbetween the spinal cord and the peripheral nerves, primarily thetortuous winding nature of peripheral nerves within their neurovascularbundles. For these reasons, the various embodiments of the implantablelead 600 discussed herein are specifically configured to have 3 or morecolumns or rows of electrodes, which are also arranged in a staggeredformation, in order to provide better a peripheral stimulation therapy.Further, the staggered electrode arrangements shown in FIGS. 10-14 allowfor formations of a plurality of different “stimulation paths” betweenthe various electrodes on the lead. These “stimulation paths” betweenthe electrodes extend in a variety of directions due to the electrodesbeing staggered, whereas the conventional neatly-arranged rows andcolumns of electrodes may allow for much fewer “stimulation paths” thatextend in different direction. Also due to the staggered electrodesherein, various “stimulation paths” may be created to generate electricfields that can be flexibly shaped. Therefore, the ability of the paddlelead herein to establish these “stimulation paths” allows for moreversatile and flexible stimulation zones and steering of stimulationover small and larger target regions, which as discussed above is aunique concern of peripheral stimulation that does not exist in thespinal cord stimulation context.

Circuit for Discriminating Between Battery Charging Signals and RFTelemetry Signals Received by a Single Coil in an Implantable MedicalDevice

As discussed above, another one of the unique aspects of the presentdisclosure is that it utilizes a single conductive element (e.g., coil)to receive different types of charging and telemetry signals andutilizes various circuit elements to provide discrimination for thesedifferent types of signals. This aspect of the present disclosure is nowdiscussed in greater detail below.

FIGS. 15A-15C provide various illustrations of a coil 700 that is anembodiment of the inductive charging component 320 and the antenna 510shown in the block diagram of FIG. 7. In other words, the coil 700 canbe used to receive both inductive charging signals (e.g., at the 13.56Mhz ISM band) and telemetry signals (e.g., at the 400 Mhz MICS band andat the 2.45 Ghz ISM band). In more detail, FIG. 15A illustrates thedisposition of the coil 700 in an embodiment of the PNS device 200, FIG.15B illustrates the coil 700 by itself, and FIG. 15C shows top views ofa few different embodiments of the coil as coil 700A, 700B, and 700C.

The coil 700 shown in FIGS. 15A and 15B in FIG. 15C are each a singleturn piece of wire having an approximately rectangular shape withrounded corners. The embodiment of the coil 700B shown in FIG. 15Cincludes an inside turn and an outside turn and thus has a slightlydifferent Q factor, inductance, and resistance compared to the singleturn embodiment of the coil 700A. The embodiment of the coil 700C shownin FIG. 15C includes two side-by-side turns and thus also has a slightlydifferent Q factor, inductance, and resistance compared to the singleturn embodiment of the coil 700A or compared to the inside/outside turnembodiment of the coil 700B. As shown in FIG. 15A, the coil 700 isimplemented outside of a hermetically-sealed housing or enclosure (alsoreferred to as a can) 710 of the PNS device 200. Most of the circuitrydiscussed above with reference to FIG. 7 are implemented within thehermetically-sealed housing 710, including but not limited to, thebattery 340, the voltage down-converter 360 and the voltage up-converter370, the microcontroller 400, the sensors 435-445, the stimulationdriver 450, the stimulation multiplexers 460, the telemetry chip 500,the circuit networks 325, 520, 530, etc.

It is understood that in these embodiments, the coil 700 is optimized toreceive signals at the 13.56 Mhz band, the 400 Mhz band, and the 2.45Ghz band, since these bands are employed to carry out the inductivecharging and telecommunications of the present embodiment of the PNSdevice 200. However, in alternative embodiments where the PNS device mayutilize different frequency bands to conduct charging andtelecommunications, the coil may be optimized differently for thosebands as well.

Conventionally, neurostimulators use an antenna to receive telemetrysignals and a separate charging coil to receive inductive chargingsignals. The antenna is typically located outside a hermetically-sealedhousing (e.g., made of metal or a metal alloy) for the pulse generator,which contains most of the circuitry such as charging circuitry,stimulation circuitry, and telemetry circuitry. The placement of theantenna outside the housing is for better signal reception. The chargingcoil is typically located inside the hermetically-sealed housing becausetraditional charging signals are limited at very low frequencies (e.g.,40 Khz-80 Khz), which can penetrate through metal relatively easily.However, the low charging frequencies are associated with a lowerquality factor (Q), which leads to charging inefficiencies. The lowcharging frequencies also require the charging coil to have many turns(e.g., 50 turns or more), which consumes a lot of space. In other words,the implementation of a signal antenna outside the housing and aseparate charging coil inside the housing results in bigger, morecumbersome neurostimulation device that may have inadequate chargingperformance.

In comparison, a single conductive element such as the coil 700 is usedto receive both telemetry signals and charging signals. The coil 700 andthe corresponding circuitry inside the PNS device 200 are configured toreceive charging signals at a much higher frequency (e.g., 13.56 Mhz)than the low charging frequencies for conventional neurostimulators. Assuch, the coil 700 can have a much higher Q than the charging coils forconventional neurostimulators. The higher Q results in better chargingefficiency and quicker charging time. In addition, since the chargingfrequency is higher, a single turn is sufficient for the coil 700, andit can be implemented outside the hermetically-sealed housing.Furthermore, the implementation of the coil 700 outside the housingreduces heating effects, and it may allow less expensive materials to beused for the housing. In some embodiments, MRI compatibility can also beenhanced, for instance, by providing no ferrite core. The material usedfor the single-turn coil 700 may also result in low resistance. The sizeof the coil 700 (e.g., due to using only a single turn wire) can also bemuch smaller than the charging coil for conventional neurostimulators.

For these reasons discussed above, the design of using a single coil forboth telemetry and charging allows the PNS device 200 to be made small,cheap, and have improved performance over conventional neurostimulators.However, since a single coil 700 is used for both telemetry andcharging, the PNS device 200 needs to be able to discriminate thetelemetry and charging signals, so that they do not cause interferencefor one another, as discussed below.

FIG. 16 is a simplified block diagram of the various components anddevices of the PNS device 200 that provide signal discrimination for thedifferent types of signals received by a single antenna. Again, it isunderstood that in the illustrated embodiment, the inductive chargingcomponent 320 and the antenna 510 shown in the block diagram of FIG. 7are integrated together as a single coil 700. The coil 700 iselectrically coupled to the circuit networks 320, 520, and 530, each ofwhich is discussed above with reference to FIG. 7. It can be seen thatthe circuit networks 320, 520, and 530 are electrically coupled inparallel. As such, the networks 320, 520, and 530 provide parallelsignal paths for different types of signals.

The circuit network 320 is coupled to the charging circuit 330 (alsodiscussed above with reference to FIG. 7) and allows inductive chargingsignals at the 13.56 Mhz band to pass through to the charging circuit330 by way of resonant network elements. In some embodiments, thecircuit network 320 includes a resonant network that generates a high Qat the resonant frequency, where the resonant frequency is tuned to besubstantially equal to the frequency of the charging signal (e.g., at13.56 Mhz). As such, the reception of signals is maximized at thecharging frequency, thereby allowing the charging signal to pass throughwith minimal attenuation. Meanwhile, although the resonant network isnot specifically configured to filter out signals from the 400 Mhz orthe 2.45 Ghz bands, the reception of the signals outside the resonantfrequency is not maximized due to the resonant frequency being at orsubstantially near the 13.56 Mhz. Thus, the resonant network of thecircuit network 320 may effectively function as a very narrow band-passfilter to “block” signals that are outside of the 13.56 Mhz band. Assuch, to the extent that the 400 Mhz and the 2.45 Ghz telemetry signalsare received by the network 320, they will be substantially attenuatedby the time they reach the charging circuit 330.

Meanwhile, the circuit networks 520 and 530 are each coupled to atelemetry chip 500 that is an embodiment of the telemetry block 500(also discussed above with reference to FIG. 7). Using filters such as aband-pass filter and a high-pass filter, the circuit network 520 allowstelemetry signals at the 400 Mhz MICS band to pass through to thetelemetry chip 500, but blocks out telemetry signals at other frequencybands (e.g., signals at the 2.45 Ghz ISM band) and inductive chargingsignals (e.g., signals at the 13.56 Mhz band). Similarly, using filterssuch as a high-pass filter, the circuit network 530 allows telemetrysignals at the 2.45 Ghz ISM band to pass through to the telemetry chip500, but blocks out telemetry signals at other frequency bands (e.g.,signals at the 400 Mhz MICS band) and inductive charging signals (e.g.,signals at the 13.56 Mhz band). Additionally, the circuit network 520and/or the circuit network 530 may include additional passive circuitelements such as inductors and/or capacitors for impedance matching, soas to maximize power transfer or to reduce signal reflection, etc. Thefiltering out of the undesired signals will minimize the interferencethat these undesired signals may cause to the desired signals.

Again, it is understood that the frequency bands used herein are merelyexamples. In other embodiments, the same approach shown in FIG. 16 maybe used to provide discrimination of other types of inductive chargingsignals and telemetry signals that may be collectively received by thesame antenna or coil. It is also understood that in a real worldimplementation, it may not be possible to completely block or filter outsignals from an undesired frequency band. Thus, in the context of thepresent disclosure, “signal blocking”, “signal filtering”, or othersimilar phrases may mean that the undesired signals are substantiallyattenuated to the point where they no longer cause any meaningfulinterference. In other words, even if some portions of the undesiredsignals may get through one of the circuit networks 320, 520, and 530discussed above, they may be negligible because their amplitudes aresufficiently small. In various embodiments, the circuit networks 320,520, and 530 may provide signal attenuations anywhere from about 10 dBto about 100 dB, for example from about 20 dB to about 60 dB.

FIG. 17 includes detailed circuit schematics of an embodiment for eachof the circuit networks 320, 520, and 530 discussed above. These circuitschematics are extracted from the circuit schematic of the PNS device200 shown in FIG. 8. In addition, to provide more clarity, simplifiedblock diagrams of the charging circuit 330 and the telemetry chip 500are appended next to the circuit schematics of the corresponding circuitnetworks 320, 520, and 530. It is also understood that a circuit node“ANT+” represents the signal line to the single antenna (or the coil 700shown in FIG. 16)

According to the embodiment shown in FIG. 17, the circuit network 320includes a series-resonant capacitor C42 and/or a parallel-resonantcapacitor 46. These resonant capacitors C42 and C46 are tuned such thatthey have a narrow resonant frequency at around 13.56 Mhz (since 13.56Mhz is the band of the inductive charging signals in this case). Asdiscussed above, the resonant capacitors C42 and C46 in effect serve asa narrow band-pass-like filter, where the pass-band is centered around13.56 Mhz. As such, the inductive charging signals of the 13.56 Mhz ISMband are able to pass through, whereas signals from other frequencybands end up being “rejected” because they are outside the resonantfrequency. In some embodiments, the series capacitor C42 may be removed,and only the parallel-resonant capacitor C46 is used to provide aresonant frequency.

The circuit network 320 further includes a diode D5 that is electricallycoupled to the capacitor C42. The diode D5 serves as a rectifyingelement. In other words, the diode D5 converts the AC inductive signalthat passes through (13.56 Mhz) into a DC signal. In other embodiments,alternative types of DC rectifiers may be used instead. The circuitnetwork 320 also includes a capacitor C43, which serves as an energystorage element herein. The inductor L5 may serve as an inductor for thebooster circuit, and the capacitor C44 may serve as a referencecapacitor for the booster circuit.

The circuit network 520 includes a band-pass filter FL1, whose pass-bandin this embodiment is centered around the 400 Mhz MICS band. Forexample, the pass-band of the band-pass filter FL1 may be fromapproximately 402 Mhz to about 405 Mhz. As such, the desired telemetrysignals in the MICS band will pass through the circuit network 520,whereas inductive charging signals and telemetry signals from otherbands will be substantially rejected. In order to provide furtherattenuation for undesired signals, the circuit network 520 also includesa high-pass filter that is formed by an inductor L2 and capacitors C1and C2. This high-pass filter is specifically targeted at the inductivecharging signals, for example signals at the 13.56 Mhz band, since theseinductive charging signals may be high in amplitude and thus warrantsfurther attenuation.

In addition, the circuit network 520 also includes passive circuitelements L1, C9, C3, and C7 that are collectively configured to optimizeimpedance matching between the antenna (coil 700) and the telemetry chip500. Again, the impedance matching provided by the passive circuitelements L1, C9, C3, and C7 may maximize power transfer (e.g., from theantenna to the telemetry chip 500 or vice versa) and/or reduce signalreflection.

The circuit network 530 includes a high-pass filter formed by aninductor L3 and capacitors C11 and C12. This high-pass filter isconfigured such that the inductive charging signals in the 13.56 Mhzband and the telemetry signals in the 400 Mhz MICS band will besubstantially rejected, but the telemetry signals in the 2.45 Ghz band(e.g., used to wake up the PNS device 200) will be allowed to passthrough.

Again, it is understood that the specific implementation of the circuitnetworks 320, 520, and 530 shown in FIG. 17 is merely an exampleimplementation. In alternative embodiments, the specific values may bechanged for the resistors, the inductors, and the capacitors shown inFIG. 17. The circuit networks 320, 520, and 530 may also includeadditional circuit elements, or some of the circuit elements may beeliminated without departing from the spirit and scope of the presentdisclosure. Furthermore, in some embodiments, digital-signal-processor(DSP) chips or other chips with advanced firmware/software may be usedto replace one or more of the circuit networks 320, 520, and 530discussed above.

FIG. 18 is a simplified flowchart of a method 800 of providingdiscrimination for a plurality of types of input signals received from asingle antenna according to an embodiment of the present disclosure. Themethod 800 includes a step 810 of receiving, via the single antenna,inductive charging signals and first telemetry signals. The inductivecharging signals are in a first frequency band, the first telemetrysignals are in a second frequency band that is substantially higher thanthe first frequency band.

The method 800 includes a step 820 of generating, via a first circuitcoupled to the single antenna, a resonant frequency substantially nearthe first frequency band such that the first circuit allows theinductive charging signals to pass through while attenuating the firsttelemetry signals.

The method 800 includes a step 830 of rejecting, via a second circuitcoupled to the single antenna, the inductive charging signals whileallowing the first telemetry signals to pass through.

In some embodiments, the first and second circuits are integrated withina hermetically-sealed housing of a peripheral nerve stimulation (PNS)device. The single antenna is located outside the hermetically-sealedhousing. The method 800 may further include the following steps:receiving, via the single antenna, second telemetry signals in a thirdfrequency band that is substantially higher than the second frequencyband; charging a battery of the PNS device in response to the receivingof the inductive charging signals; waking up stimulation circuitry ofthe PNS device in response to the receiving of the second telemetrysignals; and generating, via the stimulation circuitry, a plurality ofelectrical pulses to be delivered to a patient for an electricalstimulation therapy.

It is understood that additional process steps may be performed before,during, or after the steps 810-830. For example, the method 800 mayinclude a step of rejecting, via a third circuit coupled to the singleantenna, the inductive charging signals and the first telemetry signalswhile allowing the second telemetry signals to pass through. As anotherexample, the method 800 may include a step of matching an impedance ofthe single antenna with an impedance of a telemetry chip via a pluralityof passive circuit elements in the second circuit, wherein the secondcircuit is coupled between the single antenna and the telemetry chip.For reasons of simplicity, other additional steps are not discussedherein. In addition, the steps 810-830 need not necessarily be performedaccording to the sequence shown in FIG. 18.

Method and Apparatus of Conserving Power for an Implantable PeripheralNeurostimulator

For implantable medical devices such as peripheral neurostimulators,battery life is one of the important considerations. An implantablemedical device with poor battery life may require frequent charging,which may diminish the user's satisfaction with the implantable medicaldevice. Many conventional neurostimulators, such as spinal cordstimulators, lack optimized power management. Therefore, in spite of therelatively large size and the accompanying onboard battery with arelatively big capacity, many conventional neurostimulators have poorbattery life performance.

In comparison, the PNS device 200 of the present disclosure has aminiature size (especially compared to conventional spinal cordstimulators) and therefore a smaller battery with limited capacity.Therefore, the present disclosure employs various advanced powerconservation strategies to maximize the battery life of the PNS device200, as discussed in more detail below. The advanced power conservationstrategies lead to excellent battery performance of the PNS device 200(e.g., lasting for weeks or months without needing a charge), in spiteof its miniature size.

One of the power conservation strategies of the PNS device 200 involvesoperating the microcontroller 400 (discussed above with reference toFIG. 7) in different power modes depending on the stage of thestimulation pulse. In more detail, the microcontroller 400 offers aplurality of different operating modes, where each operating mode may beused to performance a suitable task(s) and therefore has a differentpower consumption level. Table 1. below includes a brief listing of thedifferent operating modes:

LPM4.5 AM Shut Shut Active, LPM3.5 down down FRAM LPM0 LPM1 LPM2 LPM3LPM4 RTC with w/o Mode Active off CPU Off CPU Off Standby Standby Offonly SVS SVS Maximum 16 16 MHz 16 MHz  50 kHz  50 kHz 0   50 kHz 0System MHz Clock Typical 103 65 70 μA at 35 μA at 0.7 μA 0.4 μA 0.3 μA0.25 μA  0.2 μA   0.02 μA Current μA/ μA/  1 MHz  1 MHz Consumption, MHzMHz T_(A) = 25° C. Typical N/A Instant 6 μs    6 μs  7 μs  7 μs 250 μs250 μs 1000 μs Wake-Up Time Wake-Up N/A All All LF I/O LF I/O I/O CompRTC I/O I/O Events comp comp CPU On Off Off Off Off Off Reset Reset FRAMOn Off Standby Off Off Off Off Off Off (or off) High- AvailableAvailable Available Off Off Off Reset Reset Frequency Peripherals Low-Available Available Available Available Available Off RTC ResetFrequency Peripherals Unclocked Available Available Available AvailableAvailable Available Reset Reset Pheripherals MCLK On Off Off Off Off OffOff Off SMCLK Optional Optional Optional Off Off Off Off Off ACLK On OnOn On On Off Off Off Full Yes Yes Yes Yes Yes Yes No No Retention SVSAlways Always Always Optional Optional Optional Optional On Off BrownoutAlways Always Always Always Always Always Always Always

In more detail, AM refers to an active mode of operation, where no powerconservation approaches are used. LPM0, LMP1, LPM2, LPM3, LPM4, LPM3.5,and LPM4.5 are the various power-conservation modes in which themicrocontroller 400 can operate. CPU refers to the microcontroller core410 (discussed above with reference to FIG. 7). MCLK is the main clock(clocked at 10 Mhz in this embodiment but may have a different clockrate in other embodiments, for example 20 Mhz) of the microcontroller400, ACLK is an auxiliary clock (clocked at 32.768 Khz in thisembodiment but may have a different clock rate in other embodiments) ofthe microcontroller 400, SMCLK is a sub-main clock of themicrocontroller 400, DCOCLK is a digitally-generated clock that isfeeding the main clock. In addition, DCO is a digitally-controlleroscillator, and FLL is a frequency-locked loop.

As is shown in Table 1, the microcontroller 400 turns on and off thevarious clocks and/or the peripherals of the microcontroller differentlyfor each of the operating modes. This is summarized briefly as follows:

-   -   Active mode (AM)        -   All clocks are active    -   Low-power mode 0 (LPM0)        -   CPU is disabled        -   ACLK and SMCLK remain active, MCLK is disabled        -   FLL loop control remains active    -   Low-power mode 1 (LPM1)        -   CPU is disabled        -   FLL loop control is disabled        -   ACLK and SMCLK remain active, MCLK is disabled    -   Low-power mode 2 (LPM2)        -   CPU is disabled        -   MCLK, FLL loop control, and DCOCLK are disabled        -   DCO's DC generator remains enabled        -   ACLK remains active    -   Low-power mode 3 (LPM3)        -   CPU is disabled        -   MCLK, FLL loop control, and DCOCLK are disabled        -   DCO's DC generator is disabled        -   ACLK remains active    -   Low-power mode 4 (LPM4)        -   CPU is disabled        -   ACLK is disabled        -   MCLK, FLL loop control, and DCOCLK are disabled        -   DCO's DC generator is disabled        -   Crystal oscillator is stopped    -   Complete data retention

As one example, the microcontroller 400 may operate in the LPM4power-conservation when the PNS device 200 is not in use. The LPM4 modeis also referred to as a “deep sleep” mode, where the microcontroller400 draws almost no current (i.e., consumes virtually no power). Themicrocontroller 400 has to be “woken up” from this deep sleep LPM4 modeby an external signal. By doing so, the deep sleep LPM4 mode allows themicrocontroller 400 to not waste power in standby.

As another example, the waveforms for the electrical stimulation pulsesare generated by the microcontroller 400's internal DAC(digital-to-analog converter) in real-time for each pulse. In betweenstimulation pulses—referred to as a standby period herein—themicrocontroller 400 enters one of the power-conservation modes (alsoreferred to as a low-power mode or sleep mode), for example the LPM3mode. This reduces power consumption, since many parts of themicrocontroller does not need to be turned on during the standby period.It is understood that the microcontroller 400 does not necessarily needto operate in the LPM3 throughout the entirety of the standby period inorder to realize the power savings. According to various embodiments ofthe present disclosure, the microcontroller 400 may operate in the LMP3power conservation mode in a substantial majority of the standby period,for example >75% of the standby period in some embodiments, or >90% ofthe standby period in some other embodiments, or >99% of the standbyperiod in yet some other embodiments.

When the microcontroller 400 enters the LPM3 power-conservation mode,the system clock switches from the main system clock (MCLK, which is 10MHz in this embodiment) to the crystal oscillator 430 (shown in FIG. 7)that is external to the microcontroller 400. The crystal oscillator 430has a clock frequency that is much lower than the main system clock, forexample with a clock frequency of 32.678 kHz in this case, compared tothe 10 Mhz clock frequency of the main system clock. Typically, a highclock frequency corresponds with more power consumption. Therefore,switching from a 10 Mhz clock to a 32.678 Khz clock also reduces powerconsumption.

Moreover, the microcontroller core 410 is turned off in the LPM3 mode.Meanwhile, the DMA unit 420 may be kept on (and is driven by the crystaloscillator 430) during the LPM3 mode to send instructions to variousperipherals, such as the DAC. For example, the DMA unit 420 may beconfigured to write the digital waveform data to the DAC. When thewriting of the digital waveform data into the DAC is complete, the DACoutputs the analog stimulation waveforms, i.e., the electricalstimulation pulse. Again, this process does not require themicrocontroller core 410 to be running. As discussed above, themicrocontroller core 410 is the main power-hog in the microcontroller400 and consumes substantially more power than the DMA unit 420.Consequently, turning off the microcontroller core 410, coupled with theswitching from the 10 Mhz main system clock to the 32.678 Khz clock ofthe crystal oscillator 430, allows the power consumption to be reducedfrom approximately 3 mA down to approximately 3 uA in some embodiments.In some embodiments, an interrupt signal generated by the timer unit 425(shown in FIG. 7)—clocked by the 32.768 kHz crystal oscillator 430—maybe used to wake the microcontroller 400 up from the LPM3 mode back tothe active mode in time to generate the next pulse

In addition, depending on the stimulation waveform type (active orpassive recovery), additional measures are employed to reduce powerconsumption. To illustrate, two example waveforms representing twodifferent types of a bi-phasic stimulation pulse are shown in FIGS.19-20. Specifically, the waveform in FIG. 19 shows a stimulation pulsewith a passive recovery, and the waveform in FIG. 20 shows a stimulationpulse with an active recovery. Generally, a bi-phasic stimulation pulseincludes a primary phase, an interphase, and a recovery phase. Theprimary phase is a period of time during which the actual stimulationpulse is generated. The recovery phase is a period of time to allowcharges on the electrodes to rebalance. The interphase is a period oftime between the primary phase and the recovery phase. For stimulationpulses with a passive recovery phase, the charges are passivelyrebalanced over time. In comparison, for stimulation pulses with anactive recovery phase, a “pulse” that is opposite in polarity (butsubstantially equal in amplitude) of the actual pulse (e.g., generatedin the primary phase) is generated to allow the charges to balance morequickly. Therefore, the trade-off between passive recovery and activerecovery is that passive recovery consumes less power but takes longer,and active recovery consumes more power but is quicker, which allows forstimulation at a higher frequency.

Referring now to FIG. 19, the primary phase, interphase, and the passiverecovery phase are clearly illustrated for a stimulation pulse withpassive recovery. In addition, portions of the standby period that is inbetween consecutive stimulation pulses are also illustrated. In someembodiments, the standby period may begin at the end of the recoveryphase and may last until the beginning of the primary phase for the nextpulse. It is understood that the standby period can be much longer thanthe actual pulse itself. For example, the time duration for an entirepulse—which includes the primary phase, interphase, and recoveryphase—may last from about 2 milli-seconds to about 4 milli-secondsaccording to some embodiments. In comparison, the time duration for thestandby period may last between about 1 milli-second to about 1 second.In other words, the standby period may be more than 4 to 10 times longerthan the actual pulse in some embodiments.

For most conventional neurostimulators, once a microcontroller is turnedon, it remains turned on during the stimulation pulses as well as inbetween the stimulation pulses. Stated differently, most conventionalneurostimulators keep the microcontroller turned on even during thestandby period. In comparison, the microcontroller 400 of the PNS device200 is turned on only when necessary. As FIG. 19 illustrates, themicrocontroller operates in the LPM3 power-conservation mode during mostof the standby period between consecutive stimulation pulses. Asdiscussed above, the microcontroller core 410 is turned off in the LPM3mode, which reduces power consumption significantly as themicrocontroller core 410 is a power-hungry device. Right before thepulse needs to be generated, the microcontroller 400 “wakes up” from theLPM3 power-conservation mode and begins to operate in the active mode(where the microcontroller core 410 is turned on). The waking of themicrocontroller 400 may be done by a timer signal generated by the timerunit 425, for example.

In the embodiment shown in FIG. 19, the microcontroller 400 wakes upfrom the LPM3 power-conservation mode and begins to operate in theactive mode about 100 micro-seconds before the start of the primaryphase. This is done so that the microcontroller 400 can enable thevoltage up-converter (e.g., a charge pump) 370 and the stimulationdriver 450 discussed above with reference to FIG. 7 in preparation forthe pulse generation. At some time after that, but still before thepulse is generated (before the start of the primary phase), themicrocontroller 400 sets or configures the multiplexers 460 so thatdesired stimulation channels can be formed. In the embodiment shown inFIG. 19, the multiplexers 460 are configured about 10 micro-secondsbefore the start of the primary phase.

Either the DMA unit 420 or the microcontroller core 410 may be used towrite the digital data for the stimulation waveform to the DAC. Once thedata has been completely written into the DAC, the stimulation pulse isgenerated by the DAC, thereby defining the start of the primary phase ofthe pulse. The stimulation pulse coming out of the DAC is amplified bythe stimulation driver 450 to achieve the target amplitude needed forthe peripheral stimulation therapy. In the illustrated embodiment, theamplified pulse amplitude ranges from about 0.1 V to about 12 V. Thestimulation driver 450 may also have a slew rate of about 2.3V/micro-seconds in the illustrated embodiment.

The pulse width, or the time duration of the primary phase, may beprogrammably configured. In various embodiments, the pulse width may bein a range from about 20 micro-seconds to about 2000 micro-seconds.Right before (or at) the end of the primary phase and before the startof the interphase, the multiplexers 460 are also disabled in order tofurther reduce power consumption. In the illustrated embodiment, themultiplexers 460 are disabled about 1 micro-second before the start ofthe interphase.

In the illustrated embodiment, the interphase may last for about 20micro-seconds. At the start of the interphase, or shortly after (e.g., afew micro-seconds), the voltage up-converter 370 is disabled to furtherreduce power consumption. The voltage up-converter 370 (e.g., a chargepump), when activated, supplies power to the stimulation driver 450 andthe multiplexers 460 when the stimulation pulse calls for a highervoltage than what the battery 340 can supply. For example, in thepresent embodiment, when the stimulation pulse needs to have anamplitude higher than about 3.5 V or 4 V, the battery 340 cannot supplythis high of voltage. The voltage up-converter 370 is then turned on toensure that the compliance voltage is sufficiently high. Forconventional neurostimulators, such voltage-converter (if it exists) istypically kept turned on to generate a constant high-voltage stimulationcompliance voltage, regardless of the phase of the stimulation pulse.This causes power to be wasted needlessly. In comparison, the voltageup-converter 370 of the PNS device 200 can be enabled shortly before(e.g., a few microseconds) the stimulation pulse is generated anddisabled just after (e.g., a few microseconds) the stimulation pulse isgenerated. By doing so, steady-state power consumption of the PNS device200 is reduced significantly.

Similarly, the stimulation driver 450 can be enabled shortly before(e.g., a few microseconds) the stimulation pulse is generated anddisabled shortly after (e.g., a few microseconds) the stimulation pulseis generated. Again, the timely enabling and disabling of thestimulation driver 450 prevents power from being wasted needlesslyoutside the primary phase of the stimulation pulse.

Shortly before the end of the interphase and before the start of thepassive recovery phase, the multiplexers 460 are turned on but grounded.This allows the electrical charge that has been built up on thecapacitors 465 to discharge back into the tissue. In the illustratedembodiment, the grounding of the multiplexers 460 occurs about 1micro-second before the recovery phase. The recovery phase is passivebecause the built-up charges are just “passively” being discharged toperform charge balancing, so as to achieve zero voltage on theelectrodes at the end of the passive recovery phase. In the illustratedembodiment, the passive recovery phase may last for about 2 to 6milli-seconds.

At the end (or shortly after) of the passive recovery phase, themultiplexers 460 are disabled (e.g., they may go into a high impedancemode) in order to further reduce power consumption. This marks the endof one cycle of the bi-phasic pulse, and the standby period follows theend of the previous pulse (and before the start of the subsequentpulse). To further reduce power consumption, the timer unit 425instructs the microcontroller 400 to enter or operate in the LPM3 modeagain during the standby period. This process discussed above may repeatindefinitely for each passive stimulation pulse cycle until stimulationis shut off.

Referring now to FIG. 20, the operation of the PNS device 200 for activerecovery stimulation shares many similarities with the passive recoverystimulation discussed above with reference to FIG. 19, with certaindifferences. In more detail, up to the point of the interphase, theoperation/configuration of the microcontroller 400 and the various othercomponents of the PNS device 200 are substantially identical for passiverecovery stimulation and active recovery stimulation. However, whereasthe voltage up-converter 370 and the stimulation driver 450 are disabledat or shortly after the start of the interphase for passive recoverystimulation, the voltage up-converter 370 and the stimulation driver 450remain turned on during the interphase for active recovery stimulation.In addition, whereas the multiplexers 460 are grounded before the startof the recovery phase for passive recovery stimulation, the multiplexers460 are actually configured before (e.g., about 1 milli-seconds before)the recovery phase for active recovery stimulation. These differencesreflect the fact that another pulse needs to be generated during therecovery phase for active recovery stimulation.

For example, the microcontroller core 410 or the DMA unit 420 writesdigital waveform data into the DAC during the interphase, and at thecompletion of this data writing process, the DAC outputs a stimulationpulse that is substantially equal in pulse width but opposite inpolarity with the actual stimulation pulse generated in the primaryphase. The generation of this “opposite” pulse corresponds to the activerecovery phase. The active recovery phase is thus much shorter than thepassive recovery phase, which may allow for a higher stimulationfrequency.

Since the active recovery phase require pulse generation during therecovery phase, the microcontroller 400 operates in the active mode forthe entire 3 phases of the stimulation pulse (i.e., the primary phase,the interphase, and the active recovery phase). Furthermore, the voltageup-converter 370 and the stimulation driver 450 remain turned on duringthe entire 3 phases of the stimulation pulse to ensure voltagecompliance and to amplify the stimulation pulse outputted by the DAC.

At the end of the active recovery phase, or shortly thereafter (e.g., afew micro-seconds thereafter), the multiplexers 460 are disabled, andthe voltage up-converter 370 and the stimulation driver 450 are alsodisabled. The microcontroller 400 also reverts back to the LPM3power-conservation mode after the end of the active recovery phase. Inother words, these power-consuming components are disabled in thestandby period (or at least a substantial majority thereof) betweenconsecutive pulses in order to conserve power. This process discussedabove may repeat for each active recovery stimulation pulse indefinitelyuntil stimulation is shut off.

It is understood that the active mode and the LPM3 power conservationmode are used as mere examples herein to illustrate certain aspects ofthe power reduction strategies of the PNS device 200. In otherembodiments, any of the other power-conservation modes may also beemployed to reduce power consumption. For example, in some embodiments,the microcontroller core 410 may be turned off during one or more of thephases within a pulse, and the DMA unit 420 may be used to perform othertasks instead of the microcontroller core 410, such as writing data tothe DAC.

The above discussions pertain to power reduction achieved by selectivelyoperating the microcontroller 400 in a power-conservation mode wheneverappropriate, as well as timely disabling and enabling power-consumingcomponents such as the voltage up-converter 370, the stimulation driver450, and the multiplexers 460 throughout the different phases of thestimulation pulse. In other words, the PNS device 200 micro-manages thevarious power-consuming components within to ensure that no power isneedlessly wasted.

Another example of the micromanagement used to conserve power pertainsto disconnecting the voltage up-converter 370 from its load (e.g., thestimulation driver 450 and the multiplexers 460) between consecutivestimulation pulses (i.e., during the standby period). In more detail,the voltage up-converter 370 may employ an output capacitor to storecharge. Even if the voltage up-converter 370 is turned off between thestimulation pulses (during the standby period), any load connected tothe output capacitor may still drain the charge out of the outputcapacitor. In other words, the stimulation driver 450 and themultiplexers 460 herein may serve as the load that will cause the outputcapacitor of the voltage up-converter 370 to discharge. This means thatwhen the voltage up-converter is turned on the next time, it will haveto charge up the output capacitor again, thereby wasting power.

According to various embodiments of the present disclosure, the switch480 (discussed above with reference to FIG. 7) can be used to disconnectthe stimulation driver 450 and the multiplexers 460 (i.e., the load ofthe voltage up-converter 370) from the voltage up-converter during thestandby period, even as the voltage up-converter 370, the stimulationdriver 450, and the multiplexers 460 are turned off. By timelydisconnecting the load from the voltage up-converter 370, energy (i.e.,electrical charge) stored in the voltage up-converter 370 may bepreserved for the next stimulation pulse.

It is understood that in some embodiments, the timer unit 425 (or thetimer signals generated therefrom) may be used to control the timing forthe micromanage tasks discussed above, i.e., switching themicrocontroller 400 between the active mode and one of thepower-conservation modes, enabling/disabling the voltage up-converter370, the stimulation driver 450, and the multiplexers, disconnecting theload from the voltage up-converter 370, and/or writing to the DAC. Thetimer unit 425 may be programmed by firmware or software to performthese tasks.

It is also understood that although a typical bi-phasic pulse is usedherein as an example of a stimulation pulse, the concepts discussedherein may apply to other types of stimulation pulses as well. Forexample, certain types of stimulation pulses may have a plurality ofpulses in the primary phase before the interphase and the recoveryphase. Even for these types of stimulation pulses, the microcontroller400 may still switch its mode of operation in the standby period, andthe other components such as the voltage up-converter and stimulationdrive may still be micromanaged appropriately in order to reduce powerconsumption. Furthermore, although the embodiment shown in FIGS. 19-20illustrate operating the microcontroller 400 in the active mode duringthe pulse generation, the microcontroller 400 may also operate in one ormore of the other power-conservation modes (e.g., the LPM1 mode) evenduring the pulse generation in order to further reduce powerconsumption.

FIG. 21 is a simplified flowchart of a method 900 of providing anelectrical stimulation therapy for a patient according to an embodimentof the present disclosure. The method 900 includes a step 905 ofreceiving programming instructions from an electronic programmer.

The method 900 includes a step 910 of generating, via a microcontrollerand in response to the received programming instructions, a plurality ofelectrical pulses to be delivered to the patient as a part of theelectrical stimulation therapy. Each electrical pulse includes a primaryphase, an interphase after the primary phase, and a recovery phase afterthe primary phase. Consecutive electrical pulses are separated by astandby period. The step 910 of generating of the electrical pulsescomprises: operating the microcontroller in an active mode during atleast one of: the primary phase and the interphase; and operating themicrocontroller in a power-conservation mode during a substantialmajority of the standby period. The microcontroller consumessubstantially less power when operating in the power-conservation modethan in the active mode. In some embodiments, the microcontroller is themicrocontroller 400 of FIG. 7.

The method 900 includes a step 915 of receiving an inductive energy. Insome embodiments, the inductive energy is received via a coil, forexample by the conductive charging mechanism 320 of FIG. 7 (anembodiment of which is illustrated as the coil 700 of FIGS. 15A-15C).The method 900 includes a step 920 of converting the inductive energyinto a direct current (DC) signal. In some embodiments, the convertingof the inductive energy is performed by the charging circuit 330 of FIG.7. The method 900 includes a step 925 of charging a battery with the DCsignal, thereby providing a first DC voltage via the battery. In someembodiments, the battery is the battery 340 of FIG. 7, and the firstvoltage is the output voltage of the battery 340. The method 900includes a step 930 of down-converting the first DC voltage to a secondDC voltage smaller than the first DC voltage. In some embodiments, thedown-converting is performed by the voltage down-converter 360 of FIG.7, and the second DC voltage is the output voltage of the voltagedown-converter 360. In some embodiments, the voltage down-converter 360includes a buck converter. The method 900 includes a step 935 ofproviding the second DC voltage as a voltage supply for at least themicrocontroller. The method 900 includes a step 940 of up-converting thefirst DC voltage to a third DC voltage greater than the first DCvoltage. In some embodiments, the up-converting is performed by thevoltage up-converter 370 of FIG. 7, and the third DC voltage is theoutput voltage of the up-converter 370. In some embodiments, the voltagedown-converter 370 includes a charge pump.

The method 900 includes a step 945 of providing the third DC voltage asa voltage supply for a stimulation driver and an array of multiplexerscoupled to the stimulation driver. In some embodiments, the stimulationdriver is the stimulation driver 450 of FIG. 7, and the array ofmultiplexers includes the multiplexers 460 of FIG. 7. The method 900includes a step 950 of amplifying, via the stimulation driver, theelectrical pulses generated by the microcontroller. The method 900includes a step 955 of delivering the amplified electrical pulses to thepatient at least in part by configuring the array of multiplexers. Themethod 900 includes a step 960 of disconnecting the stimulation driverfrom the voltage up-converter during the standby period betweenconsecutive electrical pulses. In some embodiments, the disconnecting isperformed at least in part by the switch 480 of FIG. 7.

In some embodiments, the microcontroller of the method 900 contains amicrocontroller core (e.g., the microcontroller core 410 of FIG. 7) anda direct memory access (DMA) unit (e.g., the DMA unit 420 of FIG. 7)that is separate from the microcontroller core and consumessubstantially less power than the microcontroller core. In theseembodiments, the operating of the microcontroller may comprises a stepof turning on the microcontroller core in the active mode, turning offthe microcontroller core in the power-conservation mode, and keeping theDMA unit turned on in the power-conservation mode. In some embodiments,the microcontroller contains a system clock that is running at a firstfrequency, and the stimulation circuitry further comprises an oscillatorthat is external to the microcontroller. The oscillator runs at a secondfrequency that is substantially lower than the first frequency. In theseembodiments, the operating of the microcontroller comprises driving themicrocontroller with the system clock in the active mode. The DMA unitis also driven with the oscillator in the power-conservation mode. Inaddition, the method 900 may include a step of generating an interruptsignal with a timer unit (e.g., the timer unit 425 of FIG. 7) that isclocked by the oscillator, and a step of waking up the microcontrollerfrom the power-conservation mode via the interrupt signal immediatelybefore a subsequent electrical pulse needs to be generated.

It is understood that the steps 905-960 need not necessarily beperformed according to the sequence shown in FIG. 21. In fact, some ofthese steps may be performed concurrently, or even in an order differentfrom what is shown in FIG. 21. It is also understood that additionalprocess steps may be performed before, during, or after the steps905-960. For example, as each electrical pulse may include either apassive recovery phase or an active recovery phase, different processsteps may be performed depending on whether the electrical pulse has apassive recovery phase or an active recovery phase. If the electricalpulse has a passive recovery phase, then the method 900 may include astep of enabling the voltage up-converter and the array of multiplexersbefore the primary phase, a step of disabling the voltage up-converterand the array of multiplexers during the interphase, and a step ofoperating the microcontroller in the power-conservation mode during thepassive recovery phase. If the electrical pulse as an active recoveryphase, then the method 900 may include a step of enabling the voltageup-converter and the array of multiplexers before the primary phase, astep of disabling the voltage up-converter and the array of multiplexersafter the active recovery phase, and a step of operating themicrocontroller in the active mode during the active recovery phase. Forreasons of simplicity, other additional steps are not discussed herein.

Charge Pump System, Devices and Methods for an Implantable Stimulator

As discussed above, the voltage up-converter 370 (shown in FIG. 7) ofthe PNS device 200 scales up the output voltage of the battery 340 toensure voltage compliance for the stimulation pulses. In more detail,the amplitude of the stimulation pulses that need to be delivered to thepatient (e.g., pulses that are amplified by the stimulation driver 450)may be greater than the voltage produced by the battery 370. In someembodiments, the stimulation pulses may vary from 0 volts to about 12volts, whereas the battery 340 can only produce up to about 4 volts. Ifthe battery 340 is configured to supply its output directly to thestimulation driver 450, the stimulation driver 450 cannot amplify thestimulation pulses to exceed the output voltage of the battery 340,thereby limiting the stimulation pulse amplitude to the output of thebattery 340. Thus, the voltage up-converter 370 is implemented to scaleup the output voltage of the battery 340 to be sufficiently high, sothat it can serve as the power supply or voltage rail of the stimulationdriver 450 without clipping the amplitude of the amplified stimulationpulses.

However, conventional voltage up-converters used for voltage compliancepurposes typically produce a scaled-up output voltage approximately onlyas an integer multiple of the input voltage. For example, ifconventional voltage up-converters are used herein, its output voltagewould be two times (2×) the output voltage of the battery 340, or threetimes (3×) the output voltage of the battery 340, etc. As such, if theoutput voltage of the battery 340 is about 4 volts, then theconventional voltage up-converter may only generate about 8 volts orabout 12 volts (or another integer multiple of 4 volts) as the voltagerail for its load (e.g., the stimulation driver 450).

While this approach described above is convenient and may ensure theintended operation of the involved devices, it is not optimized in termsof power consumption. For example, suppose the amplitude of thestimulation pulse only requires a fraction (but greater than 1) of theoutput voltage of the battery 340, for example 1.25 times of the outputvoltage of the battery 340. In other words, the output voltage of thebattery 340 is about 4 volts, and the amplitude of the stimulation pulseis about 5 volts in this example. If the conventional voltageup-conversion approach is used, then the voltage up-converter willgenerate at least 2× the output voltage of the battery 340, which willbe about 8 volts, since this is the closest integer multiple of theoutput voltage of the battery 3405 volts (or 5.1 volts if about 0.1volts of headroom is desired) for its voltage rail is unnecessary, as itwastes power needlessly. As discussed above, power consumption reductionis important for the PNS device 200 in order to achieve excellentbattery life in spite of its miniature size. Therefore, the conventionalvoltage up-conversion approach is not a good solution for the PNS device200.

According to various aspects of the present disclosure, the voltageup-converter 370 of the PNS device 200 is capable of producing ascaled-up voltage as a fraction of the input voltage (e.g., inputvoltage being the battery output voltage). The fraction may be greaterthan 1 and may vary between 1 and 2, 2 and 3, 3 and 4, etc. In thismanner, the voltage up-converter 370 can supply a voltage that istailored to the voltage rail needed for a particular stimulation pulse.By doing so, power consumption is optimized, which further improves thebattery performance of the PNS device 200.

FIG. 22A is a simplified block diagram of the voltage up-converter 370according to an embodiment of the present disclosure. In the illustratedembodiment, the voltage up-converter 370 includes a charge pump 1000.The charge pump includes a level shifter switch 1010 and a charge pumpchip 1020 coupled to the level shifter switch 1010. The level shifterswitch allows the microcontroller 400 (discussed above with reference toFIGS. 7 and 19-20) to supply the control signal VBOOST_EN (alsointerchangeably referred to as a VBOOST_EN line) to the charge pump chip1020. This is because in the illustrated embodiment, the charge pumpchip 1020 is configured to accept an input voltage of about 4 volts fromthe battery 340 (discussed above with reference to FIG. 7). However, themicrocontroller 400 in this embodiment is running at about 2.5 to about2.7 volts. Due to the voltage differences (i.e., 4 volts V.S. 2.5-2.7volts), the microcontroller 400 cannot be tied directly to the chargepump chip 1020. The level shifter switch 1010 is used to “shift up” the2.5 volts of the microcontroller 400 to the 4 volts of the battery 340,so that the microcontroller 400 can control the enabling and disablingof the charge pump chip 1020 with the VBOOST_EN control signal.

In the illustrated embodiment, the level shifter switch 1010 contains ann-type Field Effect Transistor (nFET), which is represented by D1(drain), G1 (gate), S1 (source), and a pFET, which is represented by D2(drain), G2 (gate), and S2 (source). When the nFET is enabled by theVBOOST_EN signal from the microcontroller 400, it turns on the pFET. Inother words, the gate of the pFET is pulled down when the level shifterswitch 1010 is enabled, which allows the pFET to turn on. When thishappens, the output of the battery 340 (the VBAT line) is connected topin 4 (voltage the input pin) of the charge pump chip 1020.

It is understood that the level shifter switch 1010 is not essential forthe charge pump 1000. It is implemented herein merely because themicrocontroller 400 and the battery 340 are operating at differentvoltages, and also because the charge pump chip 1020 does not have adirect enable line. Therefore, the microcontroller 400 cannot directlysupply the VBOOST_EN control signal to the charge pump chip 1020. Inother embodiments, the charge pump chip 1020 may be implemented todirectly accept the VBOOST_EN control signal (or a similar controlsignal) from the microcontroller 400, in which case the level shifterswitch 1010 may be omitted. In other words, the charge pump chip 1020 inalternative embodiments may have an input pin that can be tied directlyto the VBAT line (output voltage from the battery 340) and an enable pinthat can be tied directly to the VBOOST_EN line. When VBOOST_EN goeshigh, the charge pump chip 1020 is enabled or turned on, and it maybegin to up-convert the VBAT voltage.

Referring back to FIG. 22A, the charge pump 1000 also includes threecapacitors C29 (referred to as an input capacitor), C31 (referred to asa flying capacitor), and C30 (referred to as an output capacitor). Thesecapacitors C29, C31, and C30 are used in conjunction with the chargepump chip 1020 to boost the input voltage VBAT to a sufficiently largeoutput voltage that may serve as a compliance voltage for a load 1030.In the embodiment discussed herein, the load 1030 includes thestimulation driver 450 and the multiplexers 460 (shown in FIG. 7). Inalternative embodiments, the load 1030 may include other electricalcircuits that may draw electrical charge from the output capacitor C30.

Before the charge pump chip 1020 is enabled (e.g., by a control signalsuch as the VBOOST_EN signal), the charge pump chip 1020 is turned off,and the input capacitor C29 and the flying capacitor C31 are discharged.If the load 1030 is still connected to the charge pump chip 1020, thenthe output capacitor C30 is being discharged by the load 1020 as well.As discussed above, this is one of the reasons why the switch 480 (FIG.7) is implemented to disconnect the load 1030 from the charge pump—topreserve charges stored on the output capacitor C30 even when the chargepump is disabled (e.g., between stimulation pulses). If no load ispresent, then the output capacitor C30 is being very slowly dischargeddue to leakage current, etc., which may be negligible.

When the charge pump chip 1020 is turned on by the control signalVBOOST_EN, a clock (e.g., a 11 Khz clock in some embodiments or a 50 Khzclock in some other embodiments) inside the charge pump chip 1020 maygovern the operation of the charge pump chip 1020. For example, whenthis clock pulse is high, the charge pump chip 1020 configures its pinsso that the input capacitor C29 and the flying capacitor C31 are coupledin parallel. The capacitors C29 and C31 are each charged to the inputvoltage VBAT under this configuration. Meanwhile, the output capacitorC30 is not being charged at this time. It is understood that, thoughcapacitors typically cannot be charged up instantaneously, the chargingspeed depends on how much current can be supplied to the capacitors whenthey are being charged. In this case, the battery 340 providessufficient amount of current so as to ensure that the capacitors C29 andC31 can be fully charged to VBAT during one half of the clock cycle(i.e., when the clock pulse is high).

When the charge pump chip 1020's clock pulse goes low, the charge pumpchip 1020 reconfigures its pins so that the input capacitor C29 and theflying capacitor C31 are now coupled in series, and they arecollectively coupled in parallel with the output capacitor C30. Thiscoupling configuration allows the output capacitor C30 to be graduallycharged up by the capacitors C29 and C31. In other words, the capacitorsC29 and C31 are collective “dumping charge” into the output capacitorC30.

When the clock pulse for the charge pump chip 1020 switches to highagain, the charge pump chip 1020 again configures its pins so that theoutput capacitor C30 is disconnected from the capacitors C29 and C31,and the capacitors C29 and C31 are coupled in parallel again to becharged up to VBAT. At this time, the output capacitor C30 may dischargeinto a load (such as the load 1030), if a load is present. When theclock pulse for the charge pump chip 1020 switches to low again, thecharge pump chip 1020 reconfigures its pins so that the capacitors C29and C31 are coupled in series and collectively in parallel with theoutput capacitor C30, and the output capacitor C30 is charged up alittle more.

As the above discussions illustrate, the capacitor C30 is not completelycharged up to its full capacity in one clock cycle. Instead, thecapacitor C30 is charged up a little bit for each clock cycle (when theclock pulse goes low). Therefore, it takes a plurality of clock cyclesbefore the output capacitors C30 is fully charged up. The speed at whichthe capacitor C30 is charged up is a function of the values for thecapacitors C29, C31, and C30. As the values for the capacitors C29 andC31 decrease relative to the capacitor C30, the amount of charge dumpedinto the output capacitor C30 also decreases, and consequently it takesmore clock cycles to fully charge up the output capacitor C30. Since thecapacitor C30 is charged up by a smaller amount for each clock cycle,the charge pump 1000 may offer more granularity or a finer resolutionfor its output, which may be beneficial, as discussed below.

On the other hand, as the values for the capacitors C29 and C31 increaserelative to the capacitor C30, the amount of charge dumped into theoutput capacitor C30 also increases, and consequently it takes fewerclock cycles to fully charge up the output capacitor C30. Since thecapacitor C30 is charged up by a greater amount for each clock cycle,the charge pump 1000 may offer less granularity or a lower resolutionfor its output, but its charging speed is greater. In other words, thecharge pump 1000 may be designed and/or configured (e.g., by choosingthe values for the capacitors C29, C31, and C30) to find a desiredtradeoff balance between output voltage resolution and charging speed.Furthermore, it is understood that the capacitance value for the flyingcapacitor C31 will dominate the capacitance value C29 in determining thecharging speed of the output capacitor C30. Therefore, in someembodiments, the capacitor C29 may be omitted from consideration whendoing the output resolution V.S. charging speed tradeoff analysisdiscussed above.

In any case, when the charge pump chip 1020 is enabled, the voltage atthe output capacitor steadily increases for every clock cycle until itreaches its full capacity (2×VBAT in this case). The exact amount ofvoltage increase at the output capacitor C30 can also be calculated ormeasured. Since the clock frequency for the charge pump chip 1020 isknown (11 Khz in some embodiments or 50 Khz in some other embodiments),the pulse width or the clock period can also be calculated, which meansthat the voltage increase as a function of time can also be determined.In other words, by controlling the amount of time that the charge pumpchip 1020 is enabled, the output voltage of the charge pump chip 1020(i.e., VBOOST, which is also interchangeably referred to as the outputof the charge pump 1000 hereinafter) can be set.

As an example, suppose that it has been calculated or measured that theoutput voltage VBOOST of the charge pump chip 1020 increases as a rateof 0.5 volts per clock cycle, where the clock cycle is 11 Khz for thisexample. Thus, if a voltage of 6.5 volts is desired for VBOOST, then6.5/0.5=13 clock cycles are needed to charge the output capacitor C30 to6.5 volts. Based on a clock frequency of 11 Khz (which has a clockperiod of about 91 microseconds), it can be calculated that it wouldtake approximately 1.182 milli-seconds to charge the output capacitorC30 to 6.5 volts. The microcontroller 400 can thus be configured tocontrol the amount of time that the VBOOST_EN line is high to be about1.182 milli-seconds to achieve 6.5 volts for VBOOST.

It is understood that a load (such as the load 1030) present at theoutput of the charge pump chip 1020 may slightly affect the calculationsdiscussed above, as the load may drain the charge out of the charge pumpchip 1020, thereby decreasing its voltage. In other words, during partsof the clock cycle where the output capacitor C30 is not being charged,it may be discharged by the load 1030 if the load 1030 is connected tothe charge pump chip 1020. For example, using the above example, theVBOOST voltage at the output capacitor C30 may increase by 0.5 voltsevery clock cycle when the clock pulse is low (i.e., the capacitors C29and C31 are collectively charging up the capacitor C30), but it may alsodecrease by 0.1 volt every clock cycle when the clock pulse is high(i.e., the capacitor C30 is disconnected from the capacitors C29 andC31, which are charged up to VBAT). Based on this crude approximation,it may take 6.5/(0.5−0.1)=16.25 clock cycles are needed to charge VBOOSTto 6.5 volts, which after rounding up is 17 clock cycles. This wouldcorrespond to about 1.546 milli-seconds.

Based on the discussions above, it can be seen that the charge pump 1000of the present disclosure can achieve an output voltage VBOOST that is afraction (greater than 1) of the input voltage VBAT. The resolution ofVBOOST can also be configured in the tradeoff analysis discussed above,i.e., by configuring the capacitor values of one or more of thecapacitors C29, C31, and C30. The voltage output versatility andflexibility offered by the charge pump 1000 reduces power consumptionwaste, because it can be used to generate a customized VBOOST voltagebased on the amplitude requirement for a particular stimulation pulse ora stream of stimulation pulses.

The charge pump 1000 further includes a resistor R6 and a diode D1. Theresistor R6 serves as a “pull-up” resistor to keep the gate G2 off forthe pFET of the level shifter switch 1010. The diode D1 preventslatch-up of internal circuits of the charge pump chip 1020 when it firststarts up. It is understood that the resistor R6 and the diode D1 may beomitted in other embodiments that employ a different charge pump chip,for example one that has a direct enable line that may be tied to theVBOOST_EN line directly.

It is understood that the charge pump 1000 of FIG. 22A illustratedherein can effectively achieve an output voltage that is up to twice thebattery voltage VBAT. Referring to FIG. 22B, the circuit schematic foran alternative embodiment of the charge pump is illustrated as chargepump 1050, which can provide a voltage up to three times the batteryvoltage VBAT. In more detail, the charge pump 1050 similar to the chargepump 1000 discussed above with reference to FIG. 22A. However, adifferent charge pump chip 1060 is used. The charge pump chip 1060functions similarly to the charge pump 1020 discussed above, except thatthe charge pump chip 1060 has an enable line (SD) that is directlycontrolled by a control signal VBOOST1_EN from the microcontroller 400.This allows the charge pump chip 1060 to have its input V+ tied directlyto the VBAT input voltage. In this manner, the level shifter 1010 ofFIG. 22A is no longer needed.

Based on the operation mechanism similar to those discussed above withreference to the charge pump 1000 in FIG. 22A, the charge pump 1050 canprovide an output voltage that is up to three times of its input voltage(i.e., battery voltage VBAT). Specifically, the charge pump 1000includes a switch 1065, which is also controlled by the microcontroller400 via a control line VBOOST2_EN. If VBOOST1_EN is active (low) thenVBOOST1 outputs approximately 2×VBAT. If both VBOOST1_EN and VBOOST2_EN(high) are active, then VBOOST2 outputs approximately 3×VBAT. Again, bycarefully controlling the amount of time that the charge pump chip 1060is enabled, the charge pump 1050 can also achieve a desired fractionvalue anywhere from VBAT to 3×VBAT.

As shown in FIG. 22A, either VBAT (output from battery 340) or VBOOST(2×VBAT) may be provided to the load 1030 as a power supply. Similarly,either VBAT, VBOOST1 (2×VBAT), or VBOOST2 (3×VBAT) may be provided tothe load 1030 as a power supply. To ensure that the right voltage isselected, a corresponding circuit may be specifically configured tohandle the selection of VBAT and VBOOST in the embodiment shown in FIG.22A, or the selection of VBAT, VBOOST1, and VBOOST2 in the embodimentshown in FIG. 22B, so that the intended voltage output gets to the load1030. An example embodiment of such circuit is shown in FIG. 22C.

Referring now to FIG. 22C, a circuit 1070 is used to connect VBAT, orVBOOST1, or VBOOST2 to VCOMP (i.e., the compliance voltage or powersupply for the load 1030). In more detail, the circuit 1070 includesdiodes D4, D3, and D6. These diodes D4, D3 and D6 serve as an analog ORswitch, so that the highest of the three signals VBAT, VBOOST1, andVBOOST2 is allowed to transmit through to the VMUX line. As such, ifVBOOST1 and VBOOST2 are not enabled, then only VBAT comes through, asVBAT is the smallest voltage of the three. VBAT is used in situationswhere the stimulation driver only needs to generate a stimulation pulsesmaller than about 4 volts (i.e., stimulation pulse<=VBAT). If VBOOST1is on but VBOOST2 is off, then VBOOST1 gets connected to VMUX. SinceVBOOST1 is approximately 2×VBAT, this is used in in situations where thestimulation driver needs to generate a stimulation pulse greater thanabout 4 volts but less than about 8 volts (i.e., VBAT<stimulationpulse<=2×VBAT).

If VBOOST2 is on, then VBOOST2 gets connected to VMUX. Since VBOOST2 isapproximately 3×VBAT, this is used in in situations where thestimulation driver does not need to generate a stimulation pulse greaterthan about 8 volts but less than about 12 volts (i.e.,2×VBAT<stimulation pulse<=3×VBAT).

The circuit 1070 also includes a switch 1080. The switch 1080 iscontrolled by a control signal AMP EN from the microcontroller 400. WhenAMP EN is high, the switch 1080 connects VMUX to VCOMP, thereby allowingone of the three supply voltages (VBAT, VBOOST1, or VBOOST2) to powerthe stimulation driver or other components in the load 1030.

It is understood that a circuit similar to the circuit 1070 may beutilized to handle the selection of VBAT and VBOOST if the charge pump1000 is used. It is also understood that the specific capacitor andresistor values illustrated in FIGS. 22A-22C are mere examples and arenot intended to limit the scope of the present disclosure. Other valuesmay be used to implement alternative embodiments.

Referring now to FIG. 23, a simplified circuit schematic of the chargepump chip 1020 is illustrated. In the illustrated embodiment, the chargepump chip 1020 is implemented as the LM2767 Switched Capacitor VoltageConverter from Texas Instruments®, the data sheet of which is publishedat www.ti.com. The content of the data sheet is incorporated herein byreference in its entirety. It is understood that in the embodiment shownin FIG. 22B, the LM2765 chip from Texas Instruments® may be used toimplement the charge pump chip 1060. For reasons of simplicity, however,the circuit schematic of the LM2765 chip is not illustrated herein, butits data sheet (published as www.ti.com) is also incorporated byreference herein in its entirety).

As discussed above, conventional charge pumps that are used to scale upinput voltages typically scale up the input voltage in integermultiples. If those charge pumps are used herein, the scaled-up voltage(i.e., the compliance voltage) would be 2×VBAT, 3×VBAT, etc, but not inbetween. This leads to power waste, since compliance voltage is dictatedby the amplitude of the stimulation pulse, which could fall within anyof the integer multiples of the battery voltage VBAT.

In comparison, the charge pump 1000 (or the charge pump 1050) discussedabove allows its output voltage VBOOST (or output voltages VBOOST1 orVBOOST2 in the case of the charge pump 1050) to be dynamically adjusteddepending on the amplitude requirements of the stimulation pulse.Therefore, it is theoretically possible to change VBOOST (or VBOOST1 orVBOOST2) from pulse-to-pulse if the pulses themselves have varyingamplitudes pulse-to-pulse. In most commercially availableneurostimulators, however, the pulse amplitudes may remain constant forat least the same stimulation session. Even for these cases, the chargepump 1000 (or the charge pump 1050) can still provide a VBOOST (oroutput voltages VBOOST1 or VBOOST2 in the case of the charge pump 1050)that is specifically configured for the amplitude of the stimulationpulses throughout a particular session. As this VBOOST (or VBOOST1 orVBOOST2) may be a fraction of the input voltage VBAT, neurostimulatorswith conventional charge pump architectures may not be able to achievethe finely-tuned VBOOST (or VBOOST1 or VBOOST2) voltage, thereby wastingpower by providing a compliance voltage that may be too high for thestimulation pulses.

To better illustrate the various concepts of the charge pumps discussedabove, FIG. 24 illustrates a simplified timing graph 1100 for thewaveforms of the various signals associated with the charge pump 1000discussed above. In more detail, the timing graph 1100 includes thewaveforms for the control signal VBOOST_EN, the output voltage of thecharge pump 1000 (i.e., the output of the charge pump chip 1020) VBOOST,and the stimulation pulse voltage STIM OUT. To clarify, STIM OUT is thevoltage signal that has been amplified by the stimulation driver 450,not the stimulation pulse coming out of the DAC of the microcontroller400. These signals VBOOST_EN, VBOOST, and STIM OUT are each illustratedas a plot of an Y-axis against and X-axis, where the X-axis correspondsto time, and the Y-axis corresponds to voltage.

The control signal VBOOST_EN is enabled (i.e., goes high) before thestart of the stimulation pulse. As discussed above, VBOOST_EN turns onthe charge pump chip 1020, and the output capacitor C30 is being chargedup a little bit by the capacitors C29 and C31 for each clock cycle (theclock for the charge pump chip 1020 is not illustrated herein forreasons of simplicity). As such, as long as the charge pump chip 1020 isturned on (i.e., for the duration in which VBOOST_EN is high), VBOOSTincreases steadily until it reaches its maximum capacity (e.g., 2×VBATor 3×VBAT).

In the illustrated embodiment, VBOOST reaches a voltage 1110 whenVBOOST_EN is disabled, at which point in time the charge pump chip 1020is turned off, and VBOOST begins to drop due to the load 1030 beingconnected to the output of the charge pump 1000. The load 1030 isconnected because the stimulation driver 450 (as a part of the load1030) is amplifying the stimulation pulse outputted by the DAC. Duringthis stimulation pulse (represented by the STIM OUT waveform), thecharge pump 1000 has to supply a sufficiently high VBOOST as the voltagerail for the stimulation driver 450. As shown in FIG. 24, VBOOST dropsto a voltage 1120 at the end of the stimulation pulse.

This graph 1100 illustrate clearly that the output voltage VBOOST of thecharge pump 1000 is a function of the amount of time that it is enabled,for example as a function of the amount of time that the VBOOST_ENsignal (coming out of the microcontroller 400) is enabled. One of theunique aspects of the charge pump 1000 of the present disclosure isthat, the microcontroller 400 is configured to precisely control theamount of time that VBOOST_EN is enabled in order to produce an outputvoltage VBOOST for the charge pump 1000 that is tailored to theamplitude of the stimulation pulse.

Using this graph 1100 as an example, suppose that the stimulation pulseSTIM OUT is programmed to have a voltage amplitude of 5 volts, asrepresented by a voltage 1130 in FIG. 24. An optimized compliancevoltage in this case may be either at 5 volts or slightly exceeds 5volts to give it a little bit of head room. The head room may bepredetermined, for example it may be about 100 mV in some embodiments,in which case the optimized VBOOST may be about 5.1 volts. As shown inFIG. 24, the optimized voltage for VBOOST is represented by the voltage1120. This optimized VBOOST provides enough voltage for the circuits(e.g., op-amps) in the stimulation driver 450, and does so withoutwasting power. In comparison, a conventional voltage doubler (2×VBAT=8volts) would have wasted about 2.9 volts (8−5.1=2.9) of power.

Knowing that a 5-volt or a 5.1-volt VBOOST is desired and thus needs tobe generated by the charge pump 1000, the microcontroller 400 calculatesan amount of time 1125 that the charge pump chip 1020 needs to be turnedon (or the amount of time that VBOOST_EN needs to remain high). Incertain embodiments, the calculation for the amount of time 1125 mayalso take into account of the voltage drop of VBOOST after the chargepump chip 1020 is disabled. In other words, VBOOST_EN needs to beenabled long enough such that VBOOST reaches voltage 1110 that isadequately high, so that when it discharges over the rest of thestimulation pulse, it will not dip below the voltage 1120, which is theoptimized VBOOST voltage.

As an example, suppose that the voltage 1120 is 5.1 volts, and it hasbeen determined that the voltage drop for the rest of the stimulationpulse is about 0.5 volts, then the voltage 1110 is 5.6 volts(5.1+0.5=5.6). Again, conventional charge pumps or voltage doublerscannot produce 5.6 volts in this case, as the input voltage VBAT is 4volts. 5.6 volts would be a fraction (or a decimal) of the input voltageVBAT (1.4×VBAT in this case). The charge pump 1000 herein can producethis voltage (or very close to it, depending on the resolution ofVBOOST), and therefore the charge pump 1000 reduces power waste duringthe amplification of the stimulation pulses.

It is understood that the charge pump chip 1020 is not simply leftturned on for the entire duration of the stimulation pulse STIM OUT,which is evidenced by VBOOST_EN going low before the stimulation pulseSTIM OUT is over. The reason is that simply leaving the charge pump chip1020 turned on during the entire stimulation pulse would likely createan output voltage VBOOST that is too high, since the capacitor C30 willcontinue to be charged up as a function of time. Again, an unnecessarilyhigh VBOOST will not prevent the stimulation driver 450 from workingproperly, but it will lead to power waste in a manner similar toconventional neurostimulators. In other words, a compliance voltage thatis greater than needed would have been generated if VBOOST_EN is enabledfor the duration of the stimulation pulse.

FIG. 25 illustrates a simplified timing graph 1150 for the waveforms ofthe various signals associated with the charge pump 1000 discussed aboveaccording to an alternative embodiment. For reasons of simplicity, thesame signals and voltages appearing in both FIGS. 24 and 25 will belabeled the same.

As is shown in FIG. 25, the charge pump chip 1020 is turned on(VBOOST_EN is enabled) to charge up the output voltage VBOOST before thestimulation pulse is generated and turned off at the start of thestimulation pulse. The charge pump chip 1020 remains turned on for anamount of time 1155 that may be longer than the amount of time 1125shown in FIG. 24. This may be due to the fact that the output voltageVBOOST needs to be charged to a greater voltage 1160 to ensure that itwill still remain at or above the voltage 1120 (i.e., the optimizedcompliance voltage) throughout the stimulation pulse. Stateddifferently, the fact that the charge pump chip 1020 is turned off atthe start of the stimulation pulse leads to a longer discharge periodfor the output capacitor C30, and therefore VBOOST needs to be chargedup to a greater voltage 1160 (greater than the voltage 1110 of FIG. 24)to account for the voltage droop due to the longer discharge period.

Again, the voltage 1160 may still be a fraction (greater than 1) of theinput voltage VBAT, and therefore neurostimulators with conventionalcharge pumps or voltage doublers cannot achieve this voltage. Incomparison, the charge pump 1000 of the present disclosure can achieve avoltage close to the voltage 1160 via carefully configuring the amountof time the charge pump chip 1020 is enabled, thereby reducing waste ofpower in providing the compliance voltage for stimulation pulses.

FIG. 26 illustrates a simplified timing graph 1170 for the waveforms ofthe various signals associated with the charge pump 1000 discussed aboveaccording to yet an alternative embodiment. For reasons of simplicity,the same signals and voltages appearing in FIGS. 25-26 will be labeledthe same.

As is shown in FIG. 26, the charge pump chip 1020 is turned on(VBOOST_EN is enabled) to charge up the output voltage VBOOST before thestimulation pulse. Throughout the stimulation pulse, the charge pumpchip 1020 may be rapidly turned on and off by rapidly enabling anddisabling the VBOOST_EN line. When the charge pump chip 1020 is enabled,the output capacitor C30 is charged up a little bit, as evidenced by theoutput voltage VBOOST going up. When the charge pump chip 1020 isdisabled, the output capacitor C30 is discharged by the load 1030 alittle bit, as evidenced by the output voltage VBOOST going down.However, the enabling and disabling of the VBOOST_EN line is configuredsuch that the output voltage VBOOST does not dip below the voltage 1120,which as discussed above is the optimized compliance voltage forminimizing power consumption waste.

In addition, it is understood that the output capacitor C30 may becharged up faster than it can be discharged, or vice versa. Thus, theamount of time that the charge pump chip 1020 is turned on does notnecessarily have to be equal to the amount of time that the charge pumpchip 1020 is turned off. In other words, the VBOOST_EN line may beenabled longer than it is disabled during the stimulation pulse, or viceversa, and FIG. 26 does not intend to portray these amounts of time inscale.

It is also understood that the amount of time 1175 that charge pump chip1020 is turned on may be shorter than the amount of time 1125 shown inFIG. 24. This is because the output voltage VBOOST in this embodimentonly needs to be charged to a voltage 1180 that does not need to be ashigh as the voltage 1110 to ensure that it will still remain at or abovethe voltage 1120 (i.e., the optimized compliance voltage) throughout thestimulation pulse. Stated differently, the fact that the charge pumpchip 1020 is periodically charged during the stimulation pulse allows itto have a lower initial voltage 1180, which is still greater than thevoltage 1120, but not necessarily by much.

Again, the voltage 1180 may still be a fraction (greater than 1) of theinput voltage VBAT, and therefore neurostimulators with conventionalcharge pumps or voltage doublers cannot achieve this voltage. Incomparison, the charge pump 1000 of the present disclosure can achieve avoltage close to the voltage 1180 via carefully configuring the amountof time the charge pump chip 1020 is enabled, thereby reducing waste ofpower in providing the compliance voltage for stimulation pulses.

It is understood that FIGS. 24-26 merely illustrate various exampleembodiments of controlling the amount of time that the charging pumpchip 1020 is enabled in order to produce the desired output voltage as afraction of the input voltage. However, the concepts of the presentdisclosure are not limited to the embodiments shown in FIGS. 24-26, andthat alternative embodiments may control the timing of the signals suchas VBOOST_EN differently without departing from the spirit and scope ofthe present disclosure.

It is also understood that the graphs or waveforms similar to thoseshown in FIGS. 24-26 may be produced for the charge pump 1050 as well,to illustrate the capability of the charge pump 1050 to product avoltage that is a fraction of its input voltage. However, for reasons ofsimplicity, these graphs or waveforms are not specifically illustratedherein.

FIG. 27 is a simplified flowchart of a method 1200 of providing anelectrical stimulation therapy for a patient according to an embodimentof the present disclosure. The method 1200 includes a step 1210 ofgenerating, via a microcontroller, a plurality of electrical pulses anda control signal. In some embodiments, the microcontroller is themicrocontroller 400 of FIG. 7, the electrical pulses include the analogwaveforms outputted by the DAC onboard the microcontroller 400 of FIG.7, and the control signal includes the VBOOST_EN signal.

The method 1200 includes a step 1220 of supplying, via a battery, afirst voltage. In some embodiments, the battery is the battery 340 ofFIG. 7, and the first voltage is the output voltage of the battery 340.

The method 1200 includes a step 1230 of converting, via a voltageup-converter and in response to the control signal, the first voltage toa compliance voltage. The compliance voltage is a fraction of the firstvoltage, and wherein the fraction is greater than 1. In someembodiments, the voltage up-converter is the voltage up-converter 370 ofFIG. 7. In some embodiments, the voltage up-converter includes thecharge pump 1000 of FIG. 22. In some embodiments, the compliance voltageis the voltage supply or voltage rail for the stimulation driver 450 ofFIG. 7. In some embodiments, the converting of step 1230 comprisesdynamically adjusting the compliance voltage pulse-to-pulse in responseto respective amplitudes of the electrical pulses. In some embodiments,the converting of step 1230 comprises rapidly enabling and disabling thevoltage up-converter during the stimulation pulses.

The method 1200 includes a step 1240 of providing the compliance voltageto a stimulation driver. In some embodiments, the stimulation driver isthe stimulation driver 450 of FIG. 7. In some embodiments, the step 1240also comprises providing the compliance voltage to the multiplexers 460of FIG. 7.

The method 1200 includes a step 1250 of amplifying, via the stimulationdriver, the plurality of electrical pulses into amplified electricalpulses to be delivered to the patient as a part of the electricalstimulation therapy.

It is understood that the steps 1210-1250 need not necessarily beperformed according to the sequence shown in FIG. 27. In variousembodiments, some of these steps may be performed concurrently, or in anorder different from what is shown in FIG. 27. It is also understoodthat additional process steps may be performed before, during, or afterthe steps 1210-1250. For example, in some embodiments, the method 1200further includes a step of controlling, via the control signal, anamount of time the voltage up-converter is turned on or off. Thefraction is a function of the amount of time that the voltageup-converter is turned on. In some embodiments, the controlling theamount of time the voltage up-converter is turned on such that thecompliance voltage exceeds an amplitude of the electrical pulse by atleast a predefined headroom voltage. In some embodiments, thecontrolling the amount of time the voltage up-converter is turned onsuch that the compliance voltage exceeds an amplitude of the electricalpulse by at least a second voltage, the second voltage being a functionof a load of the voltage up-converter. For reasons of simplicity, otheradditional steps are not discussed herein.

System and Method for Improving Nerve Finding for Peripheral NerveStimulation

In peripheral nerve stimulation, finding the location of the targetednerve can be challenging when attempting to implant the therapeuticelectrodes. Several techniques are typically employed, includingsurgical exploration, ultrasonic guidance, fluoroscopic imaging, andelectrical nerve mapping. Electrical nerve mapping employs a stimulatingneedle that is introduced into the tissue while stimulating current orvoltage is delivered from the tip of the needle at a low repetitionfrequency (e.g. 2 Hz). When proximal to the targeted nerve, thestimulation current will activate the motor efferent fibers and somepart of the distal tissue will ‘twitch’ in response, following thestimulation in an expected and observable/detectable manner.

However, electrical nerve mapping is not always simple. Many minutes canbe spent seeking the nerve without success as the technique can berelatively “blind” as the nerve depth is not often known and anatomicvariability from patient to patient can result in nerve locations,and/or specific nerve target sites, that are unexpected to theimplanters. Additionally, once the nerve is found, gross motorstimulation may not be predictive of the precise location of the desiredfascicles within the nerve which innervate the painful area of thepatient. However, it is understood that pain therapy is used hereinmerely to provide an example and does not limit the concepts of thepresent disclosure.

According to various embodiments, there are provided systems, devices,and methods that can improve the likelihood and speed of finding aparticular nerve and region of the nerve for which therapeuticstimulation will be best targeted for the patient, as discussed in moredetail below with reference to FIGS. 28-31.

Referring now to FIG. 28, a simplified medical system 1300 isillustrated according to an embodiment of the present disclosure. Themedical system 1300 is configured to find the target location (e.g., aparticular fascicle) of a peripheral nerve to apply a stimulationtherapy such as electrical stimulation therapy to treat pain. Themedical system 1300 includes a stimulus generator, such as an externalpulse stimulator (EPG) 1310 (hereinafter referred to interchangeably).Similar to the IPG (e.g., the PNS device 200) discussed above, the EPG1310 may include electrical circuitry configured to generate electricalpulses, which can be applied transcutaneously or percutaneously to abody region of a patient as a part of a stimulation therapy for thepatient. In some embodiments, the therapy for the patient may be relieffrom chronic pain. In some embodiments, the therapy for the patient maybe an increase in peripheral blood flow. In yet other embodiments, thetherapy for the patient may be neuromuscular rehabilitation, needed forpost-stroke rehabilitation. In yet other embodiments, the therapy forthe patient may be incontinence associated with pelvic floor disorders.

In the illustrated embodiment, a foot 1320 is used as an example of thebody region of the patient that needs the stimulation therapy.Therefore, a transcutaneous electrical nerve stimulating patch 1330 isadhered to the foot 1320, for example near or at the center of theregion where the patient therapy is desired (e.g., where the pain is themost intense). The patch 1330 is electrically coupled to the EPG 1310and delivers the electrical pulses generated by the EPG 1310 to the foot1320 at a relatively low frequency (e.g., a few Hz or tens of Hz), forexample via one or more electrodes on the patch 1330. In someembodiments, a measurement electrode (not illustrated herein for reasonsof simplicity) is also positioned within the targeted region of therapy(e.g., the foot 1320), which can be incorporated into the stimulusgenerator or separately on a skin adhering electrode or subcutaneouselectrode.

It is understood that although an electrical-pulse generating EPG 1310is used herein as an example for providing a stimulus to a body regionof the patient as part of a patient therapy, other stimulus generatorsin alternative embodiments may be implemented differently. For example,in some embodiments, the stimulus may be mechanical, which may beadministered using a vibrator positioned within the targeted region oftherapy.

Referring back to FIG. 28, the foot 1320 contains a portion of anelongate nerve 1340. The nerve 1340 in this example is the sciaticnerve, which runs distally (after being formed from spinal nerves of thepatient's [not illustrated]), through the patient's leg, and segments ofwhich terminate within the patient's foot 1320. The stimulation therapyapplied by the EPG 1310 is targeted to the portion of the nerve 1340that resides within the foot 1320. In response to this stimulationtherapy, the electrical signals or impulses are generated and travel upthe nerve 1340 back to the spine. In some embodiments, these electricalsignals may be measured as action potentials.

A nerve-seeking needle 1350 (also referred to as a sensing needle) isintroduced in another body region 1360 that contains a different portionof the nerve 1340. The body region 1360 is a region of the body (thighin the illustrated embodiment) where implantations of anelectrode-containing lead and an IPG are desired. In other words, thebody region 1360 is chosen, based on general medical knowledge, as theimplantation site for an IPG (such as the PNS device 200) and a lead fordelivering the stimulation pulses generated by the IPG to the patient,in order to treat the pain in the foot 1320.

Based on the Gate Control Theory (the primary theoretical basis for thepain-relieving mechanism of electrical nerve stimulation), it issuggested that activation of large-diameter, heavily-myelinatedafferents that innervate a particular painful region of the body (e.g.,the foot 1320 in the illustrated embodiment) will relieve pain in thatbody area, because those large afferents increase the activity ofinhibitory interneurons in the dorsal horn of the spinal cord segment.That same spinal cord segment is generally believed to be the site wherehyperactive, pain-projecting neurons exist (either driven by smalldiameter fibers from the painful body region, or simply hyperactive dueto a prolonged state of central sensitization). Clinically, a keytechnical requirement for efficacious pain relief from electricalstimulation has been that the stimulation must generate paresthesia inthe painful region for the stimulation to be effective. In other words,if the paresthesia doesn't cover the area of pain, it is unlikely to beeffective. Therefore, when implanting peripheral nerve stimulationelectrodes, it is important to place the electrodes near the largemyelinated afferent fibers that innervate the painful regions (e.g., thefoot 1320 in the illustrated embodiment).

In this case, the large myelinated afferent fibers on the sciatic nerve1340 may be accessed by inserting the seeking needle 1350 in the bodyregion 1360 to engage (e.g., measure activity of the nerve due to closeproximity) with different fascicles of the portion of the nerve 1340 inthe body region 1360. The seeking needle 1350 receives or detects actionpotentials, such as a compound action potential (CAP), in response tothe stimulation delivered to the portion of the nerve 1340 in the foot1320 by the EPG 1310. A medical professional may operate the seekingneedle 1350 to engage different parts of the portion of the nerve 1340(e.g., different fascicles) located in the body region 1360, anddifferent action potentials may be generated and detected by the seekingneedle 1350 as a result. These action potentials may be different fromone another in terms of their amplitude, shape, timing relative to thestimulation delivered to the portion of the nerve 1340, etc.

The seeking needle 1350 is electrically coupled to a measurementinstrument 1370, for example through a physical wire or through awireless connection. The seeking needle 1350 receives the actionpotentials and sends the action potentials to the measurement instrument1370, which is configured to measure, display, and/or analyze electricalsignals, including the action potentials. In some embodiments, themeasurement instrument 1370 includes an oscilloscope. Such oscilloscopemay be configured to have a predetermined amount of gain and apredetermined bandwidth designed to capture and display the actionpotentials. In some embodiments, the measurement instrument 1370includes a dedicated monitor or visual display component. In otherembodiments, the measurement instrument 1370 may have a separate monitoror display component. The measurement instrument 1370 may also have asuitable user interface for accepting input from a user and forcommunicating an output to a user. The user interface may include atouchscreen graphical user interface, a keyboard, a mouse, speakers,etc. In some embodiments, the measurement instrument may include atransducer and a capacitively-coupled amplifier connected to a speaker,so that the action potentials may be transduced and communicated to auser in the form of audio energy. In various embodiments, themeasurement instrument 1370 may be one standalone piece of equipment(which may include several components integrated together), or it mayinclude a plurality of pieces of equipment. Via the measurementinstrument 1370, the medical professional may obtain a visual or audiblerepresentation of the action potentials detected by the needle 1350.

The system 1300 may also include a visual guidance device 1380. Thevisual guidance device 1380 may include one or more ultrasound devicesin some embodiments, or other types of medical imaging devices in otherembodiments. Using techniques such as ultrasound imaging, the visualguidance device 1380 provides crude visual guidance for a medicalprofessional who may be inserting the seeking needle 1350 into the bodyregion 1360 to engage with different parts of the nerve 1340 in thatregion.

The system 1300 may also include an indifferent electrode 1390 that iselectrically coupled to the measurement instrument 1370 but ispositioned transcutaneously or subcutaneously away from the nerve 1340and away from the body regions (e.g., the foot and the leg in thisexample) within which the nerve 1340 is contained. In some embodiments,the indifferent electrode 1390 is placed at least several tens ofcentimeters away from the target nerve and the body regions containingthe target nerve. In the illustrated embodiment, the indifferentelectrode 1390 is placed on or inside an arm of the patient. Theindifferent electrode 1390 is used as a reference for the measurement ofthe action potentials. Generally, electrical measurements such asvoltages need a reference for which the measurement is made against. Inthe context of the medical system 1300, the measurement of the actionpotentials should be made with respect to a reference that is in aregion of the volume conductor (i.e., the patient's body) that isrelatively quiet, so that it is generally not susceptible to other formsof electrical noise (e.g., noise generated by neural activity), nor doesit generate its own noise that may confound the measurement of actionpotentials herein.

In the embodiment illustrated in FIG. 28, the region that needs paintreatment is in the foot 1320 (e.g., a right foot), and the stimulationelectrodes are to be placed on or near the sciatic nerve 1340. Thus, asuitable place for the placement of the indifferent electrode 1390 is inthe skin near the patient's left forearm. The placement of theindifferent electrode 1390 in the left forearm allows it to be placedquite far from both the pain and stimulation sites (right foot and rightthigh, respectively). In addition, the indifferent electrode 1390 isalso placed far away (e.g., at least several tens of centimeters away)from areas of central conduction (spinal cord, brain), which reasonablyassures that nearly no nerve-based artifacts will be measured by theindifferent electrode 1390, which would have otherwise induced a commonmode measurement and reduced the signal detection at the nerve-seekingneedle 1350. Therefore, the use of the indifferent electrode 1390 allowsa “cleaner” and more accurate action potential to be measured by theseeking needle 1350.

According to various aspects of the present disclosure, the measurementand monitoring of the action potentials may be used to determine anoptimized site on the nerve 1340 for applying stimulation therapy. Inother words, the amplitude of any given action potential may beindicative of the effectiveness of the fascicle that gave rise to theaction potential in terms of applying stimulation therapy. In moredetail, suppose that an engagement of the seeking needle 1350 with afascicle A produced 50 micro-volts of action potential in response tothe stimulation on the foot 1320 applied by the EPG 1310, while anengagement of the seeking needle 1350 with a different fascicle Bproduced 100 micro-volts of action potential in response to the samestimulation on the foot 1320. In this example, the fascicle B is moresensitive to the stimulation received by the foot (more specifically, bythe portion of the nerve 1340 in the foot 1320), and conversely, theportion of the nerve 1340 in the foot 1320 should be more sensitive tostimulation applied through the fascicle B. This means that the fascicleB is a better conduit (i.e., a more optimized nerve site) for applyingstimulation to treat the pain at the foot 1320,

Therefore, the measurement instrument 1370 measures and monitors aplurality of different action potentials sent thereto by the seekingneedle 1350 over a period of time. Since different fascicles of thenerve 1340 are engaged over this period of time while the samestimulation is applied to the foot 1320 by the EPG 1310, the measurementinstrument 1370 receives action potentials of different sizes oramplitudes. In some embodiments, the measurement instrument 1370 may beused to record the highest or greatest action potential (which may beupdated continuously throughout this measurement and monitoringprocess). The measurement instrument 1370 may also allow the user (e.g.,the medical professional who is engaging the fascicles via the seekingneedle 1350) or an assistant to make notes as to which fascicle gaverise to the greatest action potential. In some embodiments, themeasurement instrument 1370 may record a number of candidates for the“greatest” action potential and either allows the user to manually pickwhat he/she thinks is the best one. In other embodiments, themeasurement instrument 1370 may use one or more electronic processors toexecute an algorithm or perform an analysis of the action potentials andautomatically recommend one as the best candidate. In some embodiments,the measurement instrument 1370 may also run a “moving average” of thecaptured action potentials. This “moving average” provides feedback tothe medical professional as to whether each progressive needlepositioning is getting closer to the target fascicle, or possiblyfarther away. In this manner, the maximum action potential signal duringthe nerve-seeking process may be tracked and identified.

In some embodiments, the fascicle corresponding to the greatest actionpotential may be deemed as an optimized site or target location forapply a stimulation therapy to the patient. In the context of theillustrated embodiment, it is deemed that if electrodes of a lead (andthe corresponding IPG) are implanted on such fascicle in the region1360, it will achieve the most effective stimulation results fortreating the pain in the foot 1320.

In some embodiments, once the user has found a “best site” of namednerve stimulation, the system 1300 can cease the stimulus from beingdelivered by the EPG 1310, and the nerve-seeking needle 1350 can then beused to deliver test stimulation pulses with the intent of creatingmeasurable action potentials in the region targeted for therapy. Thetest stimulation pulses may be generated by the measurement instrument1370 or by another pulse generator. Again, since the system is“connected” to both the named nerve site and the targeted region fortherapy, very small signals can be detected electronically that mightotherwise elude the visual or palpable capability of the medicalprofessional implanter or operating room staff.

The approach discussed above of finding the optimized location forimplantation of the lead is advantageous over conventional nerve seekingmethods, though it is understood that not all advantages of the presentdisclosure are necessarily discussed herein, and different embodimentsmay offer other advantages, and that no particular advantage is requiredfor all embodiments. According to conventional nerve seeking methods,the medical professional may be generally aware that a particular nervemay be stimulated to treat symptoms such as pain in a different part ofthe body. Using the example described above, the medical professionalmay recognize that, if the sciatic nerve is stimulated in the legregion, it may bring forth pain relief in the foot, since the sciaticnerve runs from the leg to the foot. However, the medical professionaldoes not know what part of the sciatic nerve (e.g., which fascicle) isthe optimized location for applying the stimulation.

As a result, the medical professionals typically employ a time-consumingtrial and error approach to determine the target nerve site forstimulation. In many cases, the patient is first sedated when a cavitywound is created to implant a lead close to a portion of the sciaticnerve in the leg, or a stimulating needle is inserted to access theportion of the sciatic nerve. Stimulation is then applied through thelead or the needle, and the medical profession attempts to observe aresponse, such as a twitch, from the foot (i.e., the part of the bodythat needs the stimulation therapy). However, even if a response fromthe foot is found, the medical professional cannot know with certaintythat the current site on the sciatic nerve really offers a sufficientamount of paresthesia for the patient. Consequently, the patient needsto be woken up to provide confirmation as to the effectiveness of thestimulation. However, the patient may be groggy from being sedated andtherefore cannot accurately report the paresthesia location in detail,if at all. In cases where the paresthesia is not sufficient or does notcover the right pain area, the medical professional may have to sedatethe patient again, reposition the lead or the stimulating needle, andwake up the patient again for confirmation. This process may need to berepeated a number of times, which can be time-consuming. Even then, theoptimized location on the nerve for applying stimulation may still notbe found. If the optimized stimulation site is not found, thestimulation therapy may not be effective, thereby decreasing patientsatisfaction with the stimulation therapy.

In comparison, the embodiments of the present disclosure use actionpotentials to determine the target site for implantation of the lead.Therefore, patient feedback—such as verbal or tactile feedback thatrequire the patient to be at least somewhat conscious and lucid—is notrequired herein. In some embodiments, the process discussed above may beperformed while the patient is sedated or under general anesthesia. Thepatient may only need to be woken up at the end (after the optimizednerve site for applying stimulation has been found) to confirm that thestimulation therapy is effective. Therefore, the nerve seeking processof the present disclosure may be performed not only more accurately, butmuch more quickly, as it relies on using electrical signals (rather thanpatient's verbal or tactile feedback) to determine the right fasciclefor applying stimulation.

Although the system 1300 may be used to perform nerve seeking while thepatient is sedated (thus requiring no patient feedback), it is alsounderstood that the patient may also be kept awake in the nerve-seekingprocess in some embodiments. For example, instead of administeringgeneral anesthesia to completely sedate the patient, a local anestheticmay be applied just to the body region 1360 where the seeking needle1350 is introduced, so as to reduce the discomfort experienced by thepatient while the needle 1350 is inserted through the skin and bodytissue and thereafter moved around to find the best nerve location. Noanesthetic needs to be applied to the foot 1320. In these embodiments,once the target site for stimulation has been selected, and teststimulation is being applied thereto, the patient may continuously orperiodically offer verbal feedback or tactile feedback as to theefficacy of the stimulation. In some embodiments, the tactile feedbackmay be offered via a patient feedback tool described in U.S. patentapplication Ser. No. 13/973,292, filed on Aug. 22, 2013, entitled“Method and System of Bracketing Stimulation Parameters on ClinicianProgrammers” to Norbert Kaula, et al., the disclosure of which is herebyincorporated by reference in its entirety. The tactile patient feedbacktool allows the patient to provide quick feedback to the medicalprofessional, which is important, as the medical professional may onlyhave a short period of time to ascertain that the lead is placedgenerally in the right location.

FIG. 29 illustrates an alternative embodiment of the medical system1300. The alternative embodiment of the medical system 1300 in FIG. 29is substantially similar to the one illustrated in FIG. 28, with anadditional telecommunications link 1395 that is coupled between the EPG1310 and the measurement instrument 1370. In some embodiments, thetelecommunications link 1395 includes a physical wire or anothersuitable physical connection. In other embodiments, thetelecommunications link 1395 may include a wireless connection betweenthe EPG 1310 and the measurement instrument 1370, for example a wirelessconnection through Wi-Fi, Bluetooth, or MICS, etc.

Communication may be conducted between the EPG 1310 and the measurementinstrument 1370 via the telecommunications link 1395. In someembodiments, the EPG 1310 generates a trigger signal and sends thetrigger signal to the measurement instrument 1370. The trigger signalmay be sent to the measurement instrument 1370 before, or substantiallysimultaneously with, the application of a pulse to the foot 1320. Thetrigger signal informs the measurement instrument 1370 that a pulse willbe (or is being) applied to the nerve 1340 in the foot 1320, and thatthe measurement instrument 1370 should be monitoring for acorrespondingly generated action potential.

Stated differently, the trigger signal may specify or define a timewindow inside which the measurement instrument 1370 should look for theaction potential. The time window may range from several micro-secondsto several tens of milli-seconds wide. Since the measurement instrument1370 now “knows” when to “expect” an incoming action potential, it mayidentify and capture action potential signals with greater accuracy. Itmay be said that the trigger signal and the stimulus delivered by theEPG 1310 constitute a “correlated activity.” Such correlated activitymay not otherwise be visually or audibly detectable by the medicalprofessional, but it can be continuously monitored or calculated by themedical system 1300. This improves the medical system 1300's ability tomeasure and monitor the action potentials.

Regardless of whether the telecommunications link 1395 is used, once atarget nerve site (e.g., a particular fascicle) has been identified asthe optimized location for applying stimulation therapy, a lead may beimplanted on this target nerve site. In some embodiments, once theseeking needle 1350 finds the target nerve site, it remains there. Apercutaneous lead with multiple electrode contacts is then threadedthrough the needle to be placed on the target nerve site. The seekingneedle 1350 is then removed without affecting the placement of thepercutaneous lead. Thereafter, a pulse generator may be coupled to thepercutaneous lead. In the case of a trialing period, an external pulsegenerator that is located outside the patient's body may be electricallycoupled to the percutaneous lead via an extension cable. In the case ofa permanent implant, the IPG (e.g., the PNS device 200) may be implantedin the body region 1360 and connected to the percutaneous lead todeliver electrical stimulation to the target nerve site through theelectrodes on the percutaneous lead. In embodiments where thepercutaneous lead includes a plurality of electrodes, the placement ofthe percutaneous lead is performed such that a middle electrode or acenter electrode on the percutaneous lead is placed right next to thetarget nerve site. This creates redundancy if the electrodes shift ormove in the future.

In some other embodiments, a paddle lead may be used to serve as thenerve seeking tool and as the electrode-containing lead to deliverstimulation once a target nerve site has been confirmed. For example,referring now to FIG. 30, a cavity may be opened up in the body region1360 to expose the portion of the sciatic nerve 1340 that resides in thebody region 1360. A paddle lead may be positioned near or on thisportion of the sciatic nerve 1340 to engage with different parts (e.g.,different fascicles) of the nerve 1340 while stimulation is applied tothe foot 1320 via the EPG 1310. In some embodiments, the paddle lead isimplemented as an embodiment of the lead 600 discussed above withreference to FIGS. 10-14, i.e., a paddle lead with staggered electrodes.Through not specifically illustrated herein for reasons of simplicity,it is understood that the paddle lead 600 is also electrically coupledto the measurement instrument 1370 shown in FIG. 28.

Similar to the seeking needle 1350, the paddle lead 600 receives theaction potentials as a result of the stimulation applied at the foot1320 and sends the action potentials to the measurement instrument 1370for monitoring and analysis. As the paddle lead 600 is moved around toengage with different nerve sites or different fascicles, differentaction potentials are received and sent to the measurement instrument1370. Similar to the embodiments in FIGS. 28-29, the measurementinstrument 1370 either allows the medical professional to manuallychoose a best action potential and the corresponding nerve site thatgave rise to the action potential, or automatically recommends one tothe medical professional. In other words, though a paddle lead 600 isused herein instead of the seeking needle 1350, the target nerve site isdetermined in a manner that is substantially similar to the embodimentswhere the seeking needle 1350 is used.

Once the target nerve site is identified, a pulse generator may becoupled to the paddle lead 600 to deliver test stimulation pulses. Insome embodiments, the measurement instrument 1370 itself may beconfigured to supply the test stimulation pulses as well. Again, if thepatient was under general anesthesia, he/she may be woken up at thistime to confirm the efficacy and coverage of the stimulation therapyapplied at this target nerve site. If the patient was only under localanesthesia, he/she does not need to be woken up and may directly providefeedback to the medical professional.

It is understood that the use of a paddle lead as both the nerve-seekingtool and the stimulation-delivering tool does not affect whether or notthe telecommunications link 1395 is implemented to send trigger signalsto the measurement instrument 1370. In other words, the trigger signalspecifying the time window inside which the action potentials should bemeasured may still be generated in embodiments where the paddle lead isused. Likewise, the indifferent electrode 1390 in FIGS. 28-29 may stillbe used to establish a “quiet” reference in the measurement of actionpotentials in embodiments where the paddle lead is used. It is alsounderstood that in some further embodiments, once a target nerve site isfound, the medical professional may be able to “mark a spot” for futureimplantation of a lead. For example, a fluorescent dye may beadministered along the length of the seeking needle 1350 and at the tipthereof, such that a subsequent surgical approach to expose the nerve ismade simple by providing a pathway toward the target nerve site.

It is understood that the foot, the leg, and the sciatic nerve are usedherein to merely provide an example to illustrate the various conceptsof the present disclosure and are not intended to be limiting. Theconcepts of the present disclosure may apply to other nerves or otherparts of the body, namely, electrical signals (e.g., action potentials)from the painful body area are used as a “beacon” to guide electrodeplacement. This allows the patient to be fully sedated in many cases,and allows for the electrode to be positioned in “real time”, i.e.,while the body area needing treatment is continuously being stimulated,so the stop-and-test approach of conventional nerve-finding methods canbe avoided.

FIG. 31 is a simplified flowchart of a method 1400 of identifying alocation for applying a stimulation therapy to treat a patient accordingto an embodiment of the present disclosure. The method 1400 includes astep 1410 of stimulating a first body region of the patienttranscutaneously via an external pulse generator (EPG). The body regioncontaining a first portion of a nerve that has an elongate shape. Themethod 1400 includes a step 1420 of sending a trigger signal to ameasurement instrument. The trigger signal defines a time window formaking a measurement. The method 1400 includes a step 1430 of measuringa plurality of different action potentials via the measurementinstrument. The measuring is performed in response to a plurality ofengagements with different fascicles of a second portion of the nervewhile the first body region is stimulated. The second portion of thenerve is in a second body region of the patient that is located remotelyfrom the first body region. In some embodiments, the measuring isperformed within the time window defined by the trigger signal. In someembodiments, the measuring is performed at least in part by using areference electrode that is placed in a third body region remotelylocated from the first body region and the second body region. Themethod 1400 includes a step 1440 of selecting, based on the measuredaction potentials, one of the fascicles that offered a greatest actionpotential as a target location of the second portion of the nerve forapplying the stimulation therapy to treat the first body region. In someembodiments, the steps 1410-1440 are performed while the patient issedated.

It is understood that the steps 1410-1440 need not necessarily beperformed according to the sequence shown in FIG. 31. In variousembodiments, some of these steps may be performed concurrently, or in anorder different from what is shown in FIG. 31. It is also understoodthat additional process steps may be performed before, during, or afterthe steps 1410-1440. For example, in some embodiments, the method 1400further includes a step of receiving the different action potentialswith one of: a seeking needle or a paddle lead. The method 1400 may alsoinclude a step of inserting a percutaneous lead through the needle, andplacing the percutaneous lead on the optimized location of the secondportion of the nerve. For reasons of simplicity, other additional stepsare not discussed herein.

Neurostimulator Configured to Sense Evoked Potentials in PeripheralNerves

Peripheral nerve stimulation is a technique for medical therapy fordifferent diseases. Depending upon the therapeutic application,peripheral nerve stimulation systems seek to activate only motor nerves(e.g., for functional purposes, such as dorsiflexion for a dropped foot,or a grasp for upper extremity hemiplegia) or only sensory nerves (e.g.,for neuropathic pain management). In any particular application, neuralselectivity is typically achieved by maximally activating the targetedfascicles while avoiding activation of those fascicles that may lead toside effects (e.g., in pain management, motor stimulation can limit theefficacy of the therapy).

In treating pain, stimulation of innocuous sensory fibers in theperiphery nerves ostensibly affects pain transmission to the brain viathe Gate Control Theory. Clinically, stimulation of these fiberstypically results in a comfortable, moderate ‘buzzing’ sensation in thearea of pain, termed paresthesia. The intensity of these sensationsrelates generally to the number and breadth of axons stimulated in thenerve, and to a lesser degree the frequency of firing of the axons.While the sensation can be comfortable for the patient, the stimulationalso provides the desired physiological effect of pain transmissioninhibition.

With implanted electrodes, however, activity by the patient (e.g., limbmovement, changes in posture, etc.) can alter the relative orientationand/or position of the electrodes or contacts with respect to thenerves. This can alter the strength of the electrical field along theaxons, and either reduce or increase the activation of the nerves.Clinically, this can be manifested as disappearance of the paresthesiaor, worse, strongly increased intensity of the paresthesia, possibly tothe point of reflexive muscle activation. These variations in thestimulation can cause the patient to use the stimulation less, and thusreduce the overall efficacy of the therapy.

What is needed includes systems, devices, and methods configured toprovide electrical nerve stimulation such that the intensity of theparesthesia sensed by a patient remains essentially constant despitebody movements or changes in position. According to various embodimentsof the present disclosure, systems, devices, and methods are providedthat are configured to sense evoked potentials generated throughelectrical stimulation of a nerve by a microstimulator+leads system,where the microstimulator+leads system is configured to reduce thevariation in stimulation sensations perceived by the patient in whom themicrostimulator+leads system is implanted and also to sense theresulting evoked potentials as surrogates for neural and physicalhealth. An evoked potential or evoked potential signal is an integratedmeasure of the conducted action potentials of a collection of nerves inresponse to stimulation. In some embodiments, the evoked potentialsignal can reflect the number of neurons activated, the fiber diameterof neurons that have been activated, the conduction velocity of theactivated neurons, etc. In some embodiments, an evoked potential signalis captured for each contact or electrode disposed along the targetnerve at a variety of stimulation pulse parameter settings. In someembodiments, these evoked potential signals can be stored as waveformsfor later retrieval, as well as for analysis of other characteristics.Time and date stamps, as well as information regarding clinical or otherconditions in existence at the time such signals were sensed and stored,may also be provided along with the evoked potentials. For the purposesof the present disclosure, the terms “evoked potentials” and “actionpotentials” or “evoked action potentials” may be used interchangeably.

In some embodiments, the microstimulator includes the PNS device 200discussed above, and the leads include one or more suitable leadsconfigured for peripheral nerve stimulation, such as a percutaneous leador a paddle lead. In some embodiments, the paddle lead may beimplemented as the paddle lead 600 (discussed above with reference toFIGS. 10-14) with the staggered electrodes arrangement. The PNS device200 and the leads are implanted inside a patient's body, and theelectrodes on the leads are configured to be positioned near a targetnerve site.

The PNS device 200 includes measurement circuitry operably coupled tothe leads, which receives sensed input signals from the leads. Thesensed input signals from the leads may include action potentials, whichmay be used as a surrogate for indicating paresthesia or othersensations experienced by the patient. In some embodiments, themeasurement circuitry may be implemented within, or as a part of, thesense amplifier 490 discussed above with reference to FIG. 7. Themeasurement circuitry routes its output to a microprocessor or othersuitable CPU, processor or controller, such as the microcontroller 400discussed above with reference to FIG. 7, or to an external processor orcontroller. The microcontroller 400 digitizes the sensed and detectedsignals for interpretation/analysis and store them in a memory or otherstorage device, which may be included in the PNS device 200 in someembodiments or remotely (such as a “cloud” server) in other embodiments.

It is understood that a processor or controller external to the PNSdevice 200 may also be able to digitize and analyze the signals from themeasurement circuitry. For example, an external programmer such as theelectronic programmer 250 discussed above with reference to FIGS. 6A-6Cmay be used to digitize or analyze the signals from the measurementcircuitry. In these embodiments, the PNS device 200 may use itstelemetry circuitry 310 (discussed above with reference to FIG. 7) totransmit the relevant information to the electronic programmer 250.

In some embodiments, the PNS device 200 monitors (for example with themeasurement circuitry) the evoked potentials periodically, for exampleon a pulse-by-pulse basis. If the PNS device 200 detects that the evokedpotentials are starting to deviate from a predefined number, it willautomatically adjust stimulation parameters to compensate for thedeviation so that the evoked potentials will return to the predefinednumber. As an example, supposed that a user (e.g., the patient himselfor a medical professional) has achieved satisfactory stimulationcoverage for the patient by configuring, via a programmer such as theelectronic programmer 200, the various stimulation parameters such asamplitude of the pulse, frequency of the pulse, or pulse width, etc. Theelectronic programmer 200 may offer the user an option to “hold stable”the stimulation, for example via a virtual or physical button on theelectronic programmer 200. In response to the user engaging the “holdstable” button, the PNS device 200 records the value of the evokedpotential at this time and stores this value in an electronic memorystorage, which may be implemented locally inside the PNS device 200 orremotely in the electronic programmer 200 or in a “cloud” server.Thereafter, the PNS device 200 will continuously (or periodically)monitor the evoked potential. If the evoked potential starts to deviatefrom the recorded value, the PNS device 200 will ramp up or downstimulation parameters such as the pulse amplitude or pulse width tocompensate for the deviation, until the measured evoked potential valuereturns to the recorded value again. In this manner, the patient mayexperience a constant level of desired sensation (e.g., comfortableparesthesia) without having to manually configure stimulationparameters.

In some embodiments, a plurality of calibration processes may beperformed to help the patient experience a constant level of comfortableparesthesia (or another sensation). For example, referring to FIGS.32A-C, several simplified waveforms are shown to provide an examplecontext of the calibration process of the present disclosure. In moredetail, FIG. 32A illustrates a simplified waveform of stimulation pulseamplitude versus time, FIG. 32B illustrates a simplified waveform ofevoked potential versus time, and FIG. 32C illustrates a simplifiedwaveform of evoked potential amplitude versus stimulation pulseamplitude.

In each calibration process, test stimulation is delivered to the targetnerve site for the patient. As the stimulation is being delivered, astimulation parameter is being ramped up or down in value. For example,the ramping up or down may include periodically adjusting the value ofthe stimulation parameter by a small predetermined step size (toward agiven direction) each time. In the illustrated embodiment, thestimulation parameter is stimulation pulse amplitude. In otherembodiments, the stimulation parameter may include a pulse width. As thevalue of the stimulation parameter is being ramped up or down, themeasurement circuitry (in conjunction with the leads) of the PNS device200 measures the amount of evoked potential in response to eachstimulation pulse that has a different value of the stimulationparameter. The patient is then prompted to indicate a plurality ofsensations experienced by the patient in response to the stimulationpulses. These sensations may include, but are not limited to: an initialperception of paresthesia, a comfortable paresthesia, an optimalparesthesia coverage for areas of pain, and an uncomfortable stimulationsensation (i.e., too much stimulation). The respective amount of themeasured evoked potential corresponding to each of the plurality ofsensations experienced by the patient and the value of the stimulationparameter that resulted in the respective amount of evoked potential isrecorded.

For example, referring to FIG. 32C, at some point during the ramping upof the stimulation pulse amplitude, the patient indicates (eitherverbally or via the patient feedback tool discussed above) that he/sheis now first experiencing paresthesia. At this point, the stimulationpulse amplitude is at 1 volt, and the PNS device 200 measures a voltageof 5 micro-volts for the evoked potential (evoked in response to the 1volt of stimulation pulse amplitude). The PNS device 200 associates thepatient's initial perception of paresthesia with the 1 volt ofstimulation pulse amplitude and the 5 micro-volts of evoked potential.This association may be recorded in an electronic storage.

As the ramping up of the stimulation pulse amplitude continues, thepatient indicates that he/she is now experiencing comfortableparesthesia. At this point, the stimulation pulse amplitude is at 2volts, and the PNS device 200 measures a voltage of 50 micro-volts forthe evoked potential. The PNS device 200 associates the patientexperiencing comfortable paresthesia with the 2 volts of stimulationpulse amplitude and the 50 micro-volts of evoked potential. Thisassociation may be recorded in an electronic storage.

As the ramping up of the stimulation pulse amplitude continues, thepatient indicates that he/she is now experiencing optimal paresthesiacoverage of the pain areas. At this point, the stimulation pulseamplitude is at 2.3 volts, and the PNS device 200 measures a voltage of60 micro-volts for the evoked potential. The PNS device 200 associatesthe patient experiencing optical paresthesia coverage of pain areas withthe 2.3 volts of stimulation pulse amplitude and the 60 micro-volts ofevoked potential. This association may be recorded in an electronicstorage.

In some embodiments, the optimal paresthesia coverage of the pain areasmay provide the patient with even better pain relief than when thepatient first experienced comfortable paresthesia. However, it isunderstood that the difference between comfortable paresthesia and theoptimal paresthesia coverage of the pain areas may not be verysignificant, and it may be subjective in some cases. Thus, the rangebetween the two may be an area of interest and may be more closelyscrutinized. For example, in some embodiments, once the comfortableparesthesia and its corresponding stimulation pulse amplitude andcorresponding evoked potential are identified, the calibration processmay “slow down,” and the ramping up may be performed with smaller stepsizes. In other words, the ramping may be performed with finerresolution to reduce the likelihood of missing a stimulation amplitudepulse (and evoked potential) for generating a best case paresthesia. Insome embodiments, a plurality of stimulation pulse amplitudes between 2to 2.3 volts and their corresponding evoked potentials between 50micro-volts and 60 micro-volts (i.e., between comfortable paresthesiaand optical paresthesia coverage) may also be recorded in the electronicstorage. These stimulation pulse amplitudes and their associated evokedpotentials may be used later as candidates for creating paresthesia.

As the ramping up of the stimulation pulse amplitude continues further,the patient indicates that he/she is now experiencing uncomfortablestimulation (i.e., due to excessive stimulation). At this point, thestimulation pulse amplitude is at 3 volts, and the PNS device 200measures a voltage of 120 micro-volts for the evoked potential. The PNSdevice 200 associates the patient experiencing optical paresthesiacoverage of pain areas with the 3 volts of stimulation pulse amplitudeand the 120 micro-volts of evoked potential. This association may berecorded in an electronic storage.

It is understood that additional patient sensations (and theircorresponding stimulation pulse amplitudes and evoked potentials) may beincluded in other embodiments. It is also understood that all thenumerical values used herein are merely for the purposes of providing anexample. In real world applications, the values of the stimulationamplitudes and evoked potentials may differ from the ones being shownherein, and they also may vary from patient to patient. It is alsounderstood that while the stimulation pulse amplitude is used herein asan example stimulation parameter that can be calibrated with respect toevoked potential and various sensations experienced by the patient,stimulation pulse width may be used as another suitable stimulationparameter to perform the calibration process discussed above.

The results of the calibration process discussed above may be used toprovide fast and automatic treatment. For example, the associations ofthe various sensations experienced by the patient and their respectivestimulation pulse amplitudes and evoked potentials may be stored in theelectronic storage onboard the PNS device 200 or on the electronicprogrammer 250. The electronic programmer 250 may present (via its userinterface) the patient (or a medical professional user) one or morestimulation programs that each correspond to one of the sensationsexperienced by the patient.

For example, the user interface may present a stimulation program (e.g.,in the form of a virtual button or icon) indicating that, if executed,will cause “comfortable paresthesia” for the patient. The stimulationprogram may retrieve the stimulation pulse amplitude (2 volts in thiscase) that led to comfortable paresthesia for the patient duringcalibration. Thus, 2 volts is used as an initial value for the pulseamplitude for generating the stimulation pulses. In addition, since 50micro-volts was recorded as the evoked potential corresponding to the“comfortable paresthesia”, the PNS device 200 may monitor the evokedpotential after the initial value of 2 volts is used for the stimulationpulse amplitude. If the detected value of the evoked potential is at 50micro-volts, the PNS device 200 continues applying stimulation with thestimulation amplitude of 2 volts. However, if the detected value of theevoked potential is lower than 50 micro-volts, the PNS device 200 mayadjust the stimulation amplitude upwards (e.g., by small step sizes)until 50 micro-volts is detected as the evoked potential again. If thedetected value of the evoked potential is higher than 50 micro-volts,the PNS device 200 may adjust the stimulation amplitude downwards (e.g.,by small step sizes) until 50 micro-volts is detected as the evokedpotential again.

Throughout this entire process, the patient need not manually program oradjust the stimulation parameters. In other words, the application ofthe stimulation program and any subsequent parameter adjustment thereofare automatic, and the stimulation program is specifically configured tore-create a sensation that the patient wants based on prior calibrationresults. Similarly, the user interface may also offer other stimulationprograms that correspond to “initial perception of paresthesia”,“optimal paresthesia coverage”, or “uncomfortable paresthesia.” Theseadditional stimulation programs may be useful in various scenarios aswell. For example, suppose that the patient is generally happy with the“comfortable paresthesia” offered by the stimulation program discussedabove but wishes to further optimize it, then the patient may executethe stimulation program corresponding to “optimal paresthesia coverage”to see if that stimulation program will offer even better pain relief.As another example, suppose that due to the passage of time, thepatient's pain has evolved to the point where 2 volts of stimulation nolonger produces comfortable paresthesia. The patient may execute thestimulation program corresponding to “initial perception ofparesthesia”, which will automatically provide a starting point or abaseline as the patient may then ramp up the stimulation pulse amplitudeto see find a better setting for providing desired pain relief.Similarly, the stimulation program corresponding to “uncomfortablestimulation” may be used to automatically generate an upper limit as thepatient ramps down the stimulation amplitude to find a better settingfor providing desired pain relief.

In all of these scenarios discussed above, the calibration results allowappropriate stimulation parameters to be automatically and quicklygenerated for a stimulation program without requiring the patient's (orthe medical professional's) input. Such stimulation program may then beexecuted to quickly re-create a prior condition in which patientexperienced a certain type of sensation. This saves time and offers moresimplicity and convenience for the patient (or other users). Inaddition, the evoked potentials are associated with different sensationsexperienced by the patient and may be used as surrogates or indicatorsfor these sensations. Once any given stimulation program is executedusing the stimulation pulse amplitude value associated with thesensation as an initial value, a servo mechanism (e.g., closed loopfeedback) may be employed to fine-tune the stimulation pulse amplitudeuntil the desired evoked potential (again, representing thecorresponding sensation of the patient) is achieved.

In some embodiments, the user interface may offer the user an option to“lock down” the stimulation parameters. In other embodiments, the userinterface may offer the user an option to “hold stable” the evokedpotential, whichever value it may be. For example, suppose that thepatient executes the stimulation program corresponding to “comfortableparesthesia” using 2 volts as the stimulation pulse amplitude, and theresulting evoked potential is measured as 55 micro-volts instead of the50-micro-volts recorded by the calibration. The patient may still findthe paresthesia generated herein very comfortable, and thus he/she maypress a “hold stable” button on the user interface of the electronicprogrammer 250. The electronic programmer 250 will then instruct the PNSdevice 200 to stop trying to adjust the stimulation parameters toproduce the 50 micro-volt evoked potential and instead maintain (oradjust if necessary) the stimulation parameters to ensure that the 55micro-volt of evoked potential is achieved.

The calibration process discussed above may be performed in a givenpatient posture state. According to the various aspects of the presentdisclosure, multiple calibration processes similar to the one discussedabove may also be performed to take into account of multiple patientposture states. For example, referring now to FIG. 33, a plurality ofexample patient posture states 1500-1540 is illustrated, though it isunderstood that these patient posture states 1500-1540 are merelyexamples and are not intended to constitute an exhaustive list ofpossible patient posture states.

In the patient posture state 1500, the patient is instruct to lie down,with at least the limb targeted for implantation of the PNS device 200and/or the leads being in a relaxed position. A first calibrationprocess similar to that discussed above with reference to FIGS. 32A-32Cmay be performed while the patient is in this patient posture state1500.

In the patient posture state 1510, the patient is instructed to dovarious stretching exercises. Specifically, the stretching exercises aredesigned to stretch the limb targeted for implantation of the PNS device200 and/or the lead. A second calibration process similar to thatdiscussed above with reference to FIGS. 32A-32C may be performed whilethe patient is in this patient posture state 1510.

In the patient posture state 1520, the patient is instructed to walkaround or otherwise become ambulatory. A third calibration processsimilar to that discussed above with reference to FIGS. 32A-32C may beperformed while the patient is in this patient posture state 1530.

In the patient posture state 1530, the patient is instructed to run. Afourth calibration process similar to that discussed above withreference to FIGS. 32A-32C may be performed while the patient is in thispatient posture state 1530. In some embodiments, the patient posturestate 1530 may be further sub-divided into a plurality of runningspeeds, for example a jogging speed and a faster sprinting speed. Thiscould be done in a controlled environment such as on a treadmill. Inthese embodiments, a calibration process may be performed for eachrunning speed.

In the patient posture state 1540, the patient is instructed to applypressure on the body region where implantation of the PNS device 200and/or the leads is targeted. For example, if the patient's left arm isthe target location for implantation of the PNS device 200 and/or theleads, the patient may be instructed to flex the muscles on the leftarm. A fifth calibration process similar to that discussed above withreference to FIGS. 32A-32C may be performed while the patient is in thispatient posture state 1540.

The results for each of the calibration processes corresponding to thedifferent patient posture states are again stored in electronic storage.Thereafter, when stimulation therapy is applied to the target nerve siteof the patient, the present patient posture state may be taken intoaccount to determine the optimal stimulation configuration for treatingthe patient. For example, suppose that based on the calibrationprocesses discussed above, it has been determined that:

-   -   while the patient is lying down, he experiences comfortable        paresthesia when a 50 micro-volt evoked potential is produced,        which according to calibration corresponds to a stimulation        pulse amplitude of 2 volts;    -   while the patient is walking around, he experiences comfortable        paresthesia when a 60 micro-volt evoked potential is produced,        which according to calibration corresponds to a stimulation        pulse amplitude of 2.5 volts; and    -   while the patient is applying pressure to the implantation site,        he experiences comfortable paresthesia when a 70 micro-volt        evoked potential is produced, which according to calibration        corresponds to a stimulation pulse amplitude of 3.0 volts.

Thereafter, in the course of normal stimulation treatment for thepatient, the PNS device 200 may detect that the patient has assumed alying down position (i.e., the patient posture state 1500). Accordingly,the PNS device 200 may generate a stimulation program using 2 volts asthe initial value for the stimulation pulse amplitude, with the goal ofachieving 50 micro-volts of evoked potential, which corresponds tocomfortable paresthesia for the patient according to calibrationresults. If the 2 volts of stimulation pulse amplitude does not quiteresult in a 50 micro-volt evoked potential, the PNS device 200 may finetune the stimulation pulse amplitude up or down (from 2 volts) until 50micro-volts of evoked potential is achieved.

Suppose that the PNS device 200 has now detected that the patient hasbegun walking around (i.e., the patient posture state 1520).Accordingly, the PNS device 200 may generate a stimulation program using2.5 volts as the initial value for the stimulation pulse amplitude, withthe goal of achieving 60 micro-volts of evoked potential, whichcorresponds to comfortable paresthesia for the patient according tocalibration results. If the 2.5 volts of stimulation pulse amplitudedoes not quite result in a 60 micro-volt evoked potential, the PNSdevice 200 may fine tune the stimulation pulse amplitude up or down(from 2.5 volts) until 60 micro-volts of evoked potential is achieved.

Suppose that the PNS device 200 has now detected that the patient hasbegun applying pressure to the implantation site (i.e., the patientposture state 1540). Accordingly, the PNS device 200 may generate astimulation program using 3.0 volts as the initial value for thestimulation pulse amplitude, with the goal of achieving 70 micro-voltsof evoked potential, which corresponds to comfortable paresthesia forthe patient according to calibration results. If the 3.0 volts ofstimulation pulse amplitude does not quite result in a 70 micro-voltevoked potential, the PNS device 200 may fine tune the stimulation pulseamplitude up or down (from 3.0 volts) until 70 micro-volts of evokedpotential is achieved.

In some embodiments, the PNS device 200 uses integrated sensors such asthe sensors 435-445 to automatically detect the patient posture state(or a change thereof). For example, the accelerometer sensor 445 may beused to detect the movement of the patient, and based on the detectedmovement, the accelerometer sensor 445 and the microcontroller 400 maycollectively determine whether the patient is lying down, or walking, orrunning. As another example, a pressure sensor may be used (inconjunction with the microcontroller 400) to detect whether the patientis applying pressure to the implantation site. In some embodiments,sensors such as accelerometers, pressure sensors, temperature sensors,etc., may also be implemented on the lead itself. This may allow formore accurate patient posture state detection.

In other embodiments, the patient may manually specify his/her currentposture state. As an example, the electronic programmer 250 may display,via its user interface, a plurality of icons or buttons, each of whichcorresponding to a respective patient posture state. The patient mayengage with these icons (such as pressing the button) as necessary toupdate his/her current posture state. The electronic programmer 250 maythen inform the PNS device 200 of the current patient posture state, sothat the PNS device 200 can generate a stimulation program tailored tosuch patient posture state based on the calibration results.

It is understood that the “brains” behind the patient posture detectionand the subsequent changing of the stimulation program may beimplemented in either the PNS device 200, or in the electronicprogrammer 250, or both, or in a remote server. For example, in someembodiments, the PNS device 200 itself may be able to determine thepatient posture state (via the onboard microcontroller and the sensors)and select a suitable stimulation program customized to the detectedpatient posture state thereafter. In some other embodiments, the PNSdevice 200 itself does not make any decisions and may merely report backto the electronic programmer 250 regarding the measurement results ofthe sensors and regarding the monitored evoked potentials. Theelectronic programmer 250 may then perform the analysis based on thedata sent by the PNS device 200 and devise a treatment plan accordingly.

Based on the discussions above, it can be seen that the multiplecalibration processes involve sensing evoked responses of nerves as asurrogate for keeping the intensity of a patient sensation (such asparesthesia) constant. This is better for patients because they mayreceive a constant amount of pain relief despite changes in position orposture, and despite limb movement, changes in limb position, limbcompression, etc. Although not discussed in detail for reasons ofsimplicity, one of ordinary skill in the art may appreciate that thevarious concepts discussed above may also apply to the detection ofdisease state, disease progression, ischemia, and/or nerve integrity orcondition.

In addition to detecting patient posture states, the sensors may providecertain other benefits. In some embodiments, the sensors may be used toavoid motor stimulation. For example, assuming that due to whateverreason—such as lead migration over time, or patient posture change, orinternal changes within the patient's body—a limb of the patient (inwhich the PNS device 200 or a lead is implanted) begins to twitchspontaneously in response to electrical stimulation. This is anunintended side effect of the stimulation therapy and is undesirable.The sensors such as the accelerometer sensor 445 may detect the twitchand report it back to the microcontroller 400. The microcontroller 400may then automatically adjust the stimulation parameters (such asdecreasing a stimulation pulse amplitude) in order to stop the twitch.This may be performed without the patient having to manually adjust thestimulation parameters, which would have taken more time (therebyprolonging the patient's discomfort), especially if the twitching isimpeding the patient from finding or operating the electronic programmer250.

In some other embodiments, the sensors may be used to providecross-checking of the evoked potential. For example, suppose that in anygiven patient posture state, the desired evoked potential has beenachieved, and the stimulation parameters have been fine-tuned tomaintain such desired evoked potential. Sometimes, when a part of thepatient's body moves—for example the limb in which the PNS device 200 orthe leads are implanted—this movement may generate an electrical signalthat may be picked up by the measurement or monitoring circuitry of thePNS device 200. This electrical signal may be misinterpreted by the PNSdevice 200 as (or part of) the evoked potential. Consequently, the PNSdevice 200 may incorrectly try to adjust the stimulation parameters totry to compensate for this “evoked potential,” when it is only temporaryand therefore warrants no adjustment of the stimulation therapy.

Here, the sensors such as the accelerometer sensor 445 may detect themovement of the patient that led to the generation of the electricalsignal. As the accelerometer sensor 445 reports this detection back tothe microcontroller 400, the microcontroller 400 may be able todetermine that the extra electrical signal is not really the evokedaction potential. The determination may be made based on the correlatedtime points in which the extra electrical signal is received and inwhich the patient movement is detected by the accelerometer sensor 445.Accordingly, the microcontroller 400 may correctly determine that theextra electrical signal is really noise and may filter it out from theevoked potential monitoring and analysis.

FIG. 34 is a simplified flowchart of a method 1600 of providing astimulation therapy to a patient according to an embodiment of thepresent disclosure. The method 1600 includes a step 1610 of performing afirst calibration process in a first patient posture state. The firstcalibration process associates a sensation experienced by a patient, inthe first patient posture state, with a first amount of an evokedpotential and a first value of a stimulation parameter for thestimulation therapy to achieve the first amount of evoked potential. Insome embodiments, the stimulation parameter includes one of: stimulationpulse amplitude or stimulation pulse width.

The method 1600 includes a step 1620 of performing a second calibrationprocess in a second patient posture state. The second calibrationprocess associates the sensation experienced by a patient, in the secondpatient posture state, with a second amount of the evoked potential anda second value of the stimulation parameter for the stimulation therapyto achieve the second amount of evoked potential.

In some embodiments, the first and second calibration processes eachinclude the following steps: delivering stimulation pulses to thepatient, wherein the delivering includes ramping up or down a value ofthe stimulation parameter; measuring a respective amount of evokedpotential in response to each stimulation pulse having a different valueof the stimulation parameter; prompting the patient to indicate aplurality of sensations experienced by the patient in response to thestimulation pulses, the plurality of sensations experienced includingparesthesia; and recording the respective amount of evoked potentialcorresponding to each of the plurality of sensations experienced by thepatient and the value of the stimulation parameter that resulted in therespective amount of evoked potential. In some embodiments, thesensations experienced by the patient comprise: initial perception ofparesthesia, comfortable paresthesia, optimal paresthesia coverage forareas of pain, and uncomfortable stimulation.

The method 1600 includes a step 1630 of storing results of the first andsecond calibration processes in an electronic storage. In someembodiments, the electronic storage resides on a neurostimulator such asthe PNS device 200 discussed above. In other embodiments, the electronicstorage resides on an electronic programmer such that the electronicprogrammer 250 discussed above. In yet other embodiments, the electronicstorage resides on a remote server (i.e., the “cloud”).

The method 1600 includes a step 1640 of detecting a current patientposture state. In some embodiments, the detecting is performedautomatically via one or more sensors and without input from thepatient. In other embodiments, the detecting is performed in response toa user selection or user input.

The method 1600 includes a decision step 1650 to determine what thecurrent patient posture state is. If it has been determined that thecurrent patient posture state is the first patient posture state, themethod 1600 proceeds to a step 1660 of applying the stimulation therapyto the patient using the first value of the stimulation parameter as aninitial value. If it has been determined that the current patientposture state is the second patient posture state, the method 1600proceeds to a step 1670 of applying the stimulation therapy to thepatient using the second value of the stimulation parameter as aninitial value.

The method 1600 also includes a step 1680 of monitoring the evokedpotential in the current patient posture state. Based on the monitoring,the step 1660 of applying the stimulation therapy in the first patientposture state includes adjusting the initial value of the stimulationparameter until the first amount of the evoked potential is reached, andthe step 1670 of applying the stimulation therapy in the second patientposture state includes adjusting the initial value of the stimulationparameter until the second amount of the evoked potential is reached.

It is understood that the steps 1610-1680 need not necessarily beperformed according to the sequence shown in FIG. 34. In variousembodiments, some of these steps may be performed concurrently, or in anorder different from what is shown in FIG. 34. It is also understoodthat additional process steps may be performed before, during, or afterthe steps 1610-1680. For example, in some embodiments, one or moreadditional calibration processes are performed in one or more additionalpatient posture states. The one or more additional calibration processeseach associate the sensation experienced by the patient, in therespective one or more additional patient posture states, with arespective amount of the evoked potential and a respective value of thestimulation parameter for the stimulation therapy to achieve therespective amount of evoked potential. If the current patient posturestate is detected as one of the one or more additional patient posturestates, a stimulation therapy is applied to the patient using thecorresponding respective value of the stimulation parameter as theinitial value. For reasons of simplicity, other additional steps are notdiscussed herein.

System and Method for Selective and Maintained Activation of SensoryPeripheral Nerve Fibers

In peripheral nerve stimulation, activation of afferent/sensory fibersis believed to be necessary to achieve pain relief, ostensibly via theGate Control Theory of pain. Most peripheral nerves, however, are mixednerves, in that they contain both sensory and motor fibers. Motor fibersare efferents, and tend to have a larger diameter and faster conductionvelocity than the neighboring sensory afferents. Activation of motorefferents can lead to uncomfortable muscle contractions that cancompromise the therapy.

Avoidance of motor efferents can be achieved by careful selection ofstimulation parameters, in particular the contact combination to focusthe stimulation field within fascicles that carry afferent sensoryinformation. However, finding the appropriate stimulation combination(and other parameters) may be a time-consuming process when the numberof stimulation contacts grows beyond four. In addition, the amplitudeand pulse width of the stimulation pulses can affect the size of thestimulation field and the locus of activated fibers.

What is needed includes methods, systems, and devices configured todetermine stimulation patterns which maximize activation of sensoryafferents while minimizing the recruitment of motor efferents.Accordingly, various embodiments of the present disclosure include analgorithm and associated methods, systems, and devices configured tomonitor the compound action potential (CAP) resulting from stimulationof a peripheral nerve and select stimulation parameters which minimizethe components of the CAP which relate to motor efferent stimulation infavor of those components of the CAP which relate to afferent sensoryfiber stimulation.

In some embodiments, a multi-contact array is placed proximal to thetargeted nerve to be stimulated. The array can be positionedlongitudinally along the axis of the nerve, with at least some contactsdistributed along the length of the nerve. In some embodiments, thestimulation is delivered on one contact, and the spatial sum of theresulting conducted action potentials (i.e., the compound actionpotential, or CAP) from the activated nerves are measured at anothercontact, at some distance away from the stimulating contact. In someembodiments, the stimulating contact may also be the measurementcontact, although this typically requires amplifier blanking and oftenmakes it difficult to see good time separation of the motor efferent andsensory afferent conducted action potentials.

FIG. 35 illustrates a graph 1700 that includes the plots of severalexample action potential signals (e.g., CAP) measured over a period oftime after a stimulus is applied. For example, the plots of signals1710-1740 each represent a respective CAP generated in response todifferent amounts of stimulation (e.g., greater stimulation pulseamplitude, or greater stimulation pulse width, or both). Generally, themotor efferents, being relatively large, fast-conducting fibers, willprimarily contribute to CAP components that are seen very soon followingthe stimulation artifact (A-alpha), and will have a relativelynarrowly-shaped complex. The sensory afferent fibers, on the other hand,are typically smaller in diameter and thus have a slower conductionvelocity. This means that their contribution to the CAP will generallyappear with greater latency following the stimulation artifact, and thecomplex will be wider (A-beta, A-gamma, etc).

In the example shown in FIG. 35, the signal 1710 is generated inresponse to a low amount of stimulation. Consequently, the A-alphacomponent (representing the motor fiber contribution to the CAP) of thesignal 1710 is beginning to show, but the A-beta and A-gamma components(representing the sensory fiber contributions to the CAP) are largelynonexistent in the signal 1710.

The signal 1720 is generated in response to a moderate amount ofstimulation that is greater than the stimulation for the signal 1720.Consequently, the A-alpha component of the signal 1720 becomes moresignificant, and the A-beta component begins to show as well. However,the A-gamma component is still largely nonexistent in the signal 1720.This means that there is some amount of sensory fiber activity inresponse to the stimulation applied to generate the signal 1720, but notvery much yet.

The signal 1730 is generated in response to a larger amount ofstimulation that is greater than the stimulation for the signal 1730. Asis shown in FIG. 35, the A-alpha component of the signal 1730 mayincrease a little bit more compared to the A-alpha component of thesignal 1720, but not by very much. However, the A-beta component of thesignal 1730 increases significantly compared to the A-beta component ofthe signal 1720. The A-gamma component is beginning to appear as well.This means that, in response to the stimulation applied to generate thesignal 1730, the sensory fiber contribution increases much more relativeto the motor fiber contribution.

The signal 1740 is generated in response to an even greater amount ofstimulation (the largest yet). However, as is shown in FIG. 35, theA-alpha and A-beta components of the signal 1740 remain almost the samecompared to the A-alpha and A-beta components of the signal 1730. TheA-gamma component increases a little bit, but not by much, and there isa low but detectable A-delta component (also representing the sensoryfiber contribution to the CAP). This means that, in response to thestimulation applied to generate the signal 1740, there is not muchimprovement in terms of maximizing the sensory fiber contribution to theCAP relative to the motor fiber contribution. In other words, eventhough stimulation strength is increased, it has reached the point ofdiminishing returns.

Based on the discussions above, it can be seen that it is beneficial toapply test stimulation with a variety of stimulation configurations(i.e., stimulation is applied differently each time), so as to discoverthe one or more stimulation configurations that offer a sensory fibercontribution to the CAP that is maximized respect to the motor fibercontribution. These stimulation configurations may then be recommendedas optimized stimulation configurations to the patient, which shouldresult in improve paresthesia with minimal side effects pertaining toundesirable motor stimulation.

In order to accurately determine the contributions to the CAP caused bythe motor fiber and by the sensory fiber component, the embodiments ofthe present disclosure establish different time windows to measure thesecontributions. Referring to FIG. 36, a graph 1800 illustrates a timewindow 1810 for capturing or measuring a motor fiber contribution 1815to the CAP, as well as a time window 1820 for capturing or measuring asensory fiber contribution 1825 to the CAP. In some embodiments, thegraph 1800 may be displayed on a measurement instrument, such as anoscilloscope or another suitable instrument.

In some embodiments, the time windows 1810 and 1820 may be establishedbased upon the assumed conduction velocity for large diameter fibers andsmall diameter fibers, as well as the known distance between thestimulating and measurement electrodes. Since large diameter fibers(i.e., motor fibers) have higher conduction velocity and small diameterfibers (i.e., sensory fibers) have lower conduction velocity, theearlier time window 1810 would capture much of the CAP waveform signaldue to large diameter motor fibers and later time windows 1820 wouldcapture CAP signals due to smaller diameter fibers. In other words, thewindow 1810 is specifically configured for capturing and measuring themotor fiber contribution to the CAP signal, and the window 1820 isspecifically configured for capturing and measuring the sensory fibercontribution to the CAP signal. Since the motor fiber contributionsignal 1815 is “expected” to be present in the time window 1810, it iseasier to identify the motor fiber contribution signal 1815 correctly(especially in situations where significant noise may be present).Likewise, the accurate identification of the sensory fiber contributionsignal 1825 is made easier by knowing its expected arrival time (i.e.,defined by the time window 1820).

In some embodiments, the time window 1810 starts at microseconds or tensof microseconds after the stimulation pulse is generated, and it has alength of about tens of milliseconds. In some embodiments, the timewindow 1820 starts at tens of milliseconds after the stimulation pulseis generated, and it has a length of about tens or hundreds ofmilliseconds. In some embodiments, the time windows 1810 and 1820 arenon-overlapping (meaning that the start of the time window 1820 occursafter the end of the time window 1810), and a separation 1830 betweenthe time windows 1810 and 1820 is in a range from about 100 microsecondsto about 5 milliseconds. In other embodiments, the time windows 1810 and1820 may partially overlap, meaning that the start of the time window1820 occurs before the end of the time window 1810.

As discussed above, in order to better distinguish the motor fiber andsensory fiber contribution signals 1815 and 1825, the measurementelectrode is typically placed far away from the stimulation electrode(though it is not necessarily required). This is because the motor fibercontribution signal 1815 travels faster than the sensory fibercontribution signal 1825. A greater distance between the stimulation andmeasurement effectively lengthens the “lag” between the motor fibercontribution signal 1815 with respect to the sensory fiber contributionsignal 1825. The greater the time separation between the signals 1815and 1825, the better the windows 1810 and 1820 can be defined and usedto capture the signals 1815 and 1825.

In the example shown in FIG. 36, the motor fiber contribution signal1815 has a narrower and taller profile, whereas the sensory fibercontribution signal 1825 has a wider and shorter profile. These signalprofiles match up with expected signal profiles for the motor fiber andsensory fiber contributions, respectively. Thus, there is a highconfidence level that these signals 1815 and 1825 indeed are the motorfiber and sensory fiber contributions, respectively. In otherembodiments, additional techniques may be used to further extract themotor fiber and sensory fiber contribution signals, including but notlimited to: template matching, peak detection, zero crossings, orcombinations thereof.

After ascertaining that the captured signals 1815 and 1825 indeed arethe motor fiber and sensory fiber contribution signals, respectively,the peak amplitudes of the signals 1815 and 1825 are measured,respectively. In this case, the motor fiber contribution signal 1815 hasan amplitude of 1840, and the sensory fiber contribution signal 1825 hasan amplitude of 1850. A ratio of the amplitude 1850 and the amplitude1840 is then calculated. For example, suppose that the amplitude 1840 is50 microvolts, and the amplitude 1850 is 25 microvolts, then a ratio ofthe amplitude 1850 and the amplitude 1840 is 0.5 (0.5=25/50). Asdiscussed above, the goal herein is to find one or more particularstimulation configuration that maximizes the sensory fiber contributionrelative to the motor fiber contribution, as that will typically lead toa more comfortable treatment for the patient.

It is also understood that the approach of measuring the sensory fiberand motor fiber contributions via the different time windows may be justan example of how to effectively measure these contributions. In otherembodiments, certain stimulation parameters may be used that are knownto be selective to different fiber types to assist in the discriminationof different CAP features. For example, a very narrow, high amplitudepulse width, known to be more selective to activating large diameter(e.g., motor) fibers may first be delivered and the resulting CAPmeasured at a distant electrode and stored by the system. Next, a widerpulse width may be used for stimulation which is known to recruit abroader spectrum of fiber diameters. The amplitude of the wider pulse isincreased until the peak amplitude of the resulting measured CAP matchesthe peak amplitude of the CAP from the narrower pulse width. This isdone since the peak amplitude of the CAP is typically due to activationof the largest diameter fibers, and, generally, a similar number oflarge diameter motor fibers will be recruited by both pulse widths whenthe peak amplitude of the CAP is about the same. The waveform differencebetween the two CAPs is then ostensibly due to activation of smallerdiameter afferents. This can also provide an estimate of the size andmorphology of the signal that will be due to activation of sensoryafferents.

According to the embodiments of the present disclosure, a predefinedalgorithm may be executed to help determine the optimized stimulationconfiguration. In some embodiments, a stimulation configuration mayinclude one or more of the following parameters: a subset of electrodeson a lead to be activated, the assigned electrode polarity for eachactivated electrode, a stimulation pulse width, and a stimulation pulseamplitude. An example algorithm is discussed below with reference toFIG. 37.

Referring to FIG. 37, an example paddle lead 1900 is shown. The paddlelead includes 16 electrodes 1-16 herein but may include any other numberof electrodes in alternative embodiments. In addition, the variousembodiments of the paddle lead 600 with staggered electrodes (shown inFIGS. 10-14) may also be used in various embodiments, as opposed to theneatly-arranged 16 electrodes aligned into 4 rows and 4 columns.Furthermore, percutaneous leads may also be used in some embodiments.

The algorithm here defines a list of electrode combinations to be testedor stepped through. In the first electrode combination, electrode 1 isfirst selected as a cathode, and its adjacent electrode 2 is selected asan anode. Generally, cathodes are the electrodes that stimulate theaxons, because cathodes have a lower activation threshold than anodes.The higher activation thresholds associated with anodes allows it tohyperpolarize a particular neuron. In other words, cathodes offer bettersensory fiber activation than anodes. Therefore, the algorithm of thepresent disclosure prioritizes finding the optimal location for cathodes(as opposed to for anodes).

With the electrode combination of electrode 1 as a cathode and electrode2 as an anode, stimulation pulse amplitude is ramped up (or down in somealternative embodiments) while pulse width is fixed. The ramping may bedone in small user-defined step sizes, and may be performedautomatically. In this manner, a plurality of stimulation configurationsare tested under this particular electrode combination (electrode 1being a cathode, and electrode 2 being an anode), where each stimulationconfiguration has a different stimulation pulse amplitude. Meanwhile,the measurement circuitry of the PNS device 200 in conjunction with thelead 1900 and the measurement instrument (e.g., oscilloscope) monitorthe motor fiber contributions and the sensory fiber contributions to theCAP, for example by measuring the motor fiber contribution signal 1815in the window 1810 and measuring the sensory fiber contribution signal1825 in the window 1820. For each different stimulation amplitude, acorresponding measurement is made as to the sizes (e.g., amplitudes 1840and 1850) of the signals 1815 and 1825, and a ratio thereof may becomputed and stored in an electronic storage, which could be onboard thePNS device 200, or on the electronic programmer 250, or in a remoteserver (i.e., the cloud).

When the stimulation pulse amplitude ramping up process is completed(for example after running through 20 different amplitudes) for theelectrode combination, the same process is repeated for a new electrodecombination. For example, electrode 1 may still be selected as acathode, but both electrodes 2 and 5 are selected as cathodes. Since theactivation of 2 cathodes may provide different activation patterns ofthe sensory and motor fibers. Again, the stimulation pulse amplitude maybe ramped up for this electrode combination while the pulse width isheld constant. The sensory fiber and motor fiber contributions are alsomeasured for each different amplitude, and the ratio thereof may becalculated and stored.

Next, the same process may be performed for yet another electrodecombination. For example, electrode 2 may be selected as a cathode,while electrodes 1 and 3 may be selected as anodes. Again, the sensoryfiber and motor fiber contributions are measured while the amplitude isbeing ramped up. This process continues until all the electrodecombinations in the predetermined list of electrode combinations havebeen exhausted. Note that the predetermined list of electrodecombinations does not include every single possible electrodecombination available, as that would have created millions of differentcombinations, which is unrealistic to try as well as unnecessary.Instead, the algorithm defines a reasonable yet likely effective list ofelectrode combinations to be stepped through.

Table 2 below lists a very simplified example of a partial list ofelectrode combinations, along with their respective stimulationamplitudes and stimulation pulse widths according to some embodiments.For reasons of simplicity, suppose that only 3 different stimulationamplitudes are being used in the ramping up process (1 mA, 2 m A, and 3mA), and that stimulation pulse width is held constant at 0.5milliseconds (ms). Again, these values are merely examples and do notnecessarily represent real world conditions.

TABLE 2 Ratio of Sensory Stimulation Stimulation Fiber ContributionPulse Pulse and Motor Cathode Anode Amplitude Width Fiber ContributionElectrode 1 Electrode 2 1 mA 0.5 ms 0.3 Electrode 1 Electrode 2 2 mA 0.5ms 0.32 Electrode 1 Electrode 2 3 mA 0.5 ms 0.4 Electrode 1 Electrodes 2and 5 1 mA 0.5 ms 0.42 Electrode 1 Electrodes 2 and 5 2 mA 0.5 ms 0.31Electrode 1 Electrodes 2 and 5 3 mA 0.5 ms 0.42 Electrode 2 Electrodes 1and 3 1 mA 0.5 ms 0.5 Electrode 2 Electrodes 1 and 3 2 mA 0.5 ms 0.51Electrode 2 Electrodes 1 and 3 3 mA 0.5 ms 0.52 Electrode 2 Electrodes1, 3, and 6 1 mA 0.5 ms 0.53 Electrode 2 Electrodes 1, 3, and 6 2 mA 0.5ms 0.55 Electrode 2 Electrodes 1, 3, and 6 3 mA 0.5 ms 0.56 Electrode 3Electrodes 2 and 4 1 mA 0.5 ms 0.72 Electrode 3 Electrodes 2 and 4 2 mA0.5 ms 0.76 Electrode 3 Electrodes 2 and 4 3 mA 0.5 ms 0.78 Electrode 3Electrodes 2, 4 and 7 1 mA 0.5 ms 0.71 Electrode 3 Electrodes 2, 4 and 72 mA 0.5 ms 0.77 Electrode 3 Electrodes 2, 4 and 7 3 mA 0.5 ms 0.84Electrode 4 Electrodes 3 and 8 1 mA 0.5 ms 0.64 Electrode 4 Electrodes 3and 8 2 mA 0.5 ms 0.65 Electrode 4 Electrodes 3 and 8 3 mA 0.5 ms 0.67Electrode 5 Electrodes 1 and 9 1 mA 0.5 ms 0.43 Electrode 5 Electrodes 1and 9 2 mA 0.5 ms 0.41 Electrode 5 Electrodes 1 and 9 3 mA 0.5 ms 0.45Electrode 5 Electrodes 1, 9 and 6 1 mA 0.5 ms 0.51 Electrode 5Electrodes 1, 9 and 6 2 mA 0.5 ms 0.57 Electrode 5 Electrodes 1, 9 and 63 mA 0.5 ms 0.53 Electrode 6 Electrodes 5 and 7 1 mA 0.5 ms 0.44Electrode 6 Electrodes 5 and 7 2 mA 0.5 ms 0.43 Electrode 6 Electrodes 5and 7 3 mA 0.5 ms 0.45 Electrode 6 Electrodes 5, 7, and 10 1 mA 0.5 ms0.47 Electrode 6 Electrodes 5, 7, and 10 2 mA 0.5 ms 0.48 Electrode 6Electrodes 5, 7, and 10 3 mA 0.5 ms 0.49 . . . . . . . . . . . . . . .Electrode 16 Electrodes 12 and 15 1 mA 0.5 ms 0.21 Electrode 16Electrodes 12 and 15 2 mA 0.5 ms 0.23 Electrode 16 Electrodes 12 and 153 mA 0.5 ms 0.26 Electrode 16 Electrodes 12, 15, and 11 1 mA 0.5 ms 0.31Electrode 16 Electrodes 12, 15, and 11 2 mA 0.5 ms 0.32 Electrode 16Electrodes 12, 15, and 11 3 mA 0.5 ms 0.36

Essentially, each row of Table 2 constitutes a unique stimulationconfiguration. It is only partial because not every single electrodecombination is shown for reasons of simplicity (i.e., the electrodecombinations in which electrodes 7-15 are assigned as cathodes are notshown). It is also simplified since a real world stimulation pulseamplitude ramping process will likely include more than just 3 steps. Inaddition, the pulse width here is held constant to simplify thealgorithm, though a person of ordinary skill in the art would recognizethat it is possible for the pulse width to be ramped along with, orseparately from the stimulation pulse amplitude herein.

In any case, the ratio of the sensory fiber contribution and the motorfiber contribution is computed and recorded for each stimulationconfiguration. According to Table 2, a best ratio of 0.84 is obtainedunder the stimulation configuration in which the electrode combinationhas the electrode 3 as a cathode, and electrodes 2, 4, and 7 as anodes,with a stimulation pulse amplitude of 3 mA, and a pulse width of 0.5 ms.This particular stimulation configuration may then be automaticallyrecommended (e.g., by the electronic programmer 250) as an optimizedstimulation configuration to use in order to maximize the sensory fibercontribution relative to the motor fiber contribution, which facilitatesmore comfortable stimulation treatment for the patient.

In some embodiments, several stimulation configurations are chosen aspossible candidates to be recommended as the optimized stimulationconfigurations. For example, the stimulation configurations (i.e., rowsin Table 2) corresponding to the ratio of 0.77 and 0.78 are alsorecorded as these possible candidates, since they result in a ratio ofsensory fiber contribution relative to the motor fiber contribution thatis also pretty high. In some embodiments, after the top 3 or 4stimulation configurations “candidates” are identified, the algorithmmay ramp up or down the stimulation pulse width for these 3 or 4 topstimulation configuration “candidates.” At the end of that process, thebest candidate may be chosen to be the one that is recommended.

In some embodiments, the algorithm may include two or more stages. In acoarse testing stage, the algorithm steps through the stimulationconfigurations in a coarse manner, where there is not much resolutionbetween the stimulation pulse amplitudes, or pulse width, or evenelectrode combination selection. For example, the stimulation pulseamplitude may have just 2 or 3 different values. After the initialcoarse testing process is performed, several top stimulationconfigurations are selected based on their ratios of sensory fibercontribution to the motor fiber contribution. Thereafter, in a finetesting stage, the testing is performed for these candidates with finerresolution, for example by ramping up the stimulation pulse amplitude orpulse width with 20 or 30 different values. This multi-stage approachmay save time and may yield the desired result quickly and accurately.

It is understood that the above example illustrate using a ratio (i.e.,relative size) of the sensory fiber contribution and the motor fibercontribution to the CAP as a gauge of determining a particularstimulation configuration's effectiveness in maximizing the sensoryfiber contribution relative to the motor fiber contribution (orminimizing the motor fiber contribution relative to the sensory fibercontribution). However, in alternative embodiments, the absolute sizesof the sensory fiber and motor fiber contributions may also be usedinstead of, or in addition to, the relative sizes of the sensory fiberand motor fiber contributions to the CAP.

It is also understood that the above testing process may be performed inan automated manner without requiring the patient's verbal or tactilefeedback. For example, after the implantation surgery, the patient goesto the clinic for a follow up visit. The medical professional mayattempt to optimize the stimulation parameters in this visit. Accordingto the embodiments of the present disclosure, the algorithm may beloaded onto the PNS device 200 and executed. Once it begins theexecution, the patient can sit back and relax. He/she may feel differentamounts of paresthesia and in different regions of the body, but he/sheunderstands that it is a result of the various different stimulationconfigurations being applied. A measurement instrument configured tomeasure action potentials is coupled to the PNS device (either through awire or wirelessly). Thus, the sensory fiber and motor fibercontributions are measured and recorded at least partially via themeasurement instrument.

As discussed above, the values (either absolute or relative) of thesensory fiber and motor fiber contributions to the CAP as used assurrogates of the patient's paresthesia (or perception of theparesthesia). Since these values can be generated and measuredautomatically by machines, the verbal and/or tactile feedback from theactual patient is no longer needed. This saves a great deal of time, asconventional methods require the patient's indication of whether aparticular stimulation configuration is effective or not, which createsa long time lag between the execution of each possible stimulationconfiguration. Since the patient's time and the medical professional'stime are limited during the patient's visit, the long lag and slowexecution of the stimulation configurations under the conventionalapproach means that often times the best (or at least optimized)stimulation configurations may not be found. In comparison, theautomated execution of the algorithm and the feedback obtained from themeasurement machines (and without needing patient feedback) means that amuch more exhaustive list of stimulation configurations may be tested,thereby increasing the likelihood of discovering one or more optimizedstimulation configurations that provide very good treatment for thepatient, even if they may or may not be theoretically “the best.”

In some embodiments, the transition between the contact combinations ismade time-efficient. For example, while one contact combination is beingevaluated, the next contact combination in the queue is readied and isactivated at a low amplitude (eg, 50% of the paresthesia threshold ofthe combination under test). When the testing of the present contactcombination is complete, the subject is then guided to increase the mAuntil they feel a nominal paresthesia. Testing of this formerly queuedcontact combination is then implemented and the next combination in thequeue is similarly readied.

It is also understood that the algorithm may be executed when thepatient is in actual surgery too. Regardless of the setting or contextin which the algorithm is executed, the end result is that one or moreoptimized stimulation configurations may be automatically recommended,either to the patient or to the medical professional. In someembodiments, the recommendation may be done via the electronicprogrammer 250, for example in the form of one or more automaticallycreated stimulation programs that each correspond to the one or moreoptimized stimulation configurations. It is also understood that invarious embodiments, the algorithm and the execution results may bestored on the PNS device 200, or on the electronic programmer 250, or inthe cloud.

In some embodiments, the algorithm consistently monitors the CAP resultof the stimulation pulses, ideally on a pulse-by-pulse basis, but thefrequency of electrical CAP measurement can be reduced. If the ratio ofsensory afferent CAP component to motor efferent CAP component changes,or the motor efferent CAP becomes too large, then the algorithm canautomatically alter the amplitude or pulse width of the stimulation, orgradually transition the present contact combination to another contactcombination which was previously among those which maximize sensory CAPand minimize the motor CAP component.

In some embodiments, the algorithm can monitor the amplitude of thesensory CAP component, and, if it decreases, then the stimulationamplitude may be automatically increased to try to maintain it asconstant and vice-versa. In this manner, the sensory CAP component canbe held fixed by a closed-loop algorithm which does so by titrating theamplitude and/or pulse width, which ostensibly will keep any sensationsand therapeutic effect constant in the face of body or limb motion.

In some embodiments, motor activity resulting from reflex activation(i.e., sensory stimulation which, in the spinal cord, triggers motorneuron activity) can also be monitored. In such an algorithm, the windowfor evaluating the response to intended sensory stimulation is delayedmore from the stimulation pulse than in some of the above examples. Fastconducting responses (again, defined by narrow complexes or multiplecomplexes) that have originated in the spine are looked for in thiswindow. Depending upon the algorithm, if reflex motor efferent activityis observed, this, too, may be used to select ‘best’ contactcombinations, i.e., those that minimize these reflex signals or theratio of these reflex signals to the sensory afferent components. Insome embodiments, if these signals are seen, the amplitude and/or pulsewidth of the stimulation is adjusted automatically by the algorithm.

FIG. 38 is a simplified flowchart of a method 2000 of providing astimulation therapy to a patient according to an embodiment of thepresent disclosure. The method 2000 includes a step 2010 of deliveringelectrical stimulation to a nerve site of the patient. The electricalstimulation is delivered using a stimulation configuration with respectto one or more of the following: activation of a subset of a pluralityof electrodes on a lead, electrode polarity for the activatedelectrodes, stimulation pulse width, and stimulation pulse amplitude.

The method 2000 includes a step 2020 of measuring an action potentialevoked from the nerve site in response to the electrical stimulation.The action potential includes a sensory fiber contribution and a motorfiber contribution, and wherein the measuring comprises measuring thesensory fiber contribution and the motor fiber contribution. In someembodiments, the step 2020 includes measuring the motor fibercontribution within a first time window, and measuring the sensory fibercontribution within a second time window, the second time window being alater time window than the first time window.

The method 2000 includes a decision step 2030 to determine whetherenough stimulation configurations has been tested or stepped through. Ifthe answer from the decision step 2030 is no, then the method 2000 loopsback to the step 2010 again. Thus, the steps 2010 and 2020 may beperformed a plurality of cycles, where each cycle is performed using adifferent stimulation configuration. In some embodiments, the repeatedexecution of steps 2010 and 2020 may be performed according to apredefined algorithm that specifies the activation of electrodes,electrode polarity, the stimulation pulse width, and the stimulationpulse amplitude for each cycle. In some embodiments, the algorithm mayinclude the following steps: selecting an electrode combination thatspecifies a subset of electrodes to be activated and a respectiveelectrode polarity for each activated electrode; ramping up or down thestimulation pulse amplitude for the selected electrode combination; andrepeating the selecting and the ramping a plurality of times until apredetermined list of electrode combinations have been exhausted,wherein a different electrode combination is selected each time. In someembodiments, the selecting, the ramping, and the repeating are performedwhile holding the stimulation pulse width constant. In theseembodiments, the algorithm may further include a step of picking, afterthe exhaustion of the predetermined list of electrode combinations, oneor more electrode combinations with their corresponding stimulationamplitudes that maximized the sensory fiber contribution. The algorithmmay also include a step of ramping the stimulation pulse width for theone or more electrode combinations. In some embodiments, the electrodecombinations in the predetermined list each include a different cathode.If the answer from the decision step 2030 is yes—meaning that asufficient number of stimulation configurations has been tested orstepped through—then the method 2000 continues with a step 2040 ofrecommending, as a candidate for optimized stimulation configuration,the stimulation configuration that offers a greatest sensory fibercontribution relative to the motor fiber contribution. In someembodiments, the various steps of the method 2000 are performed withoutrequiring verbal or tactile feedback from the patient.

It is understood that the steps 2010-2080 need not necessarily beperformed according to the sequence shown in FIG. 38. In variousembodiments, some of these steps may be performed concurrently, or in anorder different from what is shown in FIG. 38. It is also understoodthat additional process steps may be performed before, during, or afterthe steps 2010-2040. For reasons of simplicity, these additional stepsare not discussed herein.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: applying electricalstimulation to a patient at least in part via a pulse generator;measuring a motor fiber component of an action potential that is evokedin response to the electrical stimulation; measuring a sensory fibercomponent of the action potential; and determining a relationshipbetween the motor fiber component and the sensory fiber component. 2.The method of claim 1, further comprising: estimating a paresthesia ofthe patient based on the determining.
 3. The method of claim 1, whereinthe determining comprises: calculating a ratio between the sensory fibercomponent and the motor fiber component.
 4. The method of claim 1,wherein the determining comprises: comparing absolute sizes of thesensory fiber component and the motor fiber component.
 5. The method ofclaim 1, further comprising: repeating the applying of the electricalstimulation, the measuring of the motor fiber component, the measuringof the sensory fiber component, and the determining the relationshipbetween the motor fiber component and the sensory fiber component aplurality of times, wherein a different set of stimulation parameters isused for each of the times; and selecting one or more of the sets ofstimulation parameters as optimized sets of stimulation parameters basedon the determined relationship between the motor fiber component and thesensory fiber component for each of the times.
 6. The method of claim 1,wherein: the measuring of the motor fiber component is performed withina first time window; and the measuring of the sensory fiber component isperformed within a second time window that occurs after the first timewindow.
 7. The method of claim 1, wherein the applying of the electricalstimulation, the measuring of the motor fiber component, the measuringof the sensory fiber component, and the determining the relationshipbetween the motor fiber component and the sensory fiber component areperformed when the patient is in actual surgery.
 8. The method of claim1, wherein the applying of the electrical stimulation, the measuring ofthe motor fiber component, the measuring of the sensory fiber component,and the determining the relationship between the motor fiber componentand the sensory fiber component are performed in an automated mannerwithout requiring a voluntary feedback from the patient.
 9. A medicalsystem, comprising: a pulse generator configured to apply electricalstimulation to a patient; a measurement tool configured to measure amotor fiber component and a sensory fiber component of an actionpotential that is evoked from in response to the electrical stimulation;and an electronic processor configured to determine a relationshipbetween the motor fiber component and the sensory fiber component. 10.The medical system of claim 9, wherein the electronic processor isfurther configured to estimate a paresthesia of the patient based on thedetermined relationship between the motor fiber component and thesensory fiber component.
 11. The medical system of claim 9, wherein theelectronic processor is further configured to calculate a ratio betweenthe sensory fiber component and the motor fiber component.
 12. Themedical system of claim 9, wherein: the pulse generator is configured toapply a plurality of cycles of electrical stimulation, wherein adifferent set of stimulation parameters is used in each cycle; themeasurement tool is configured to measure the motor fiber component andthe sensory fiber component corresponding to each cycle; and theelectronic processor is configured to determine the relationship betweenthe motor fiber component and the sensory fiber component correspondingto each cycle.
 13. The medical system of claim 12, wherein theelectronic processor is configured to select one or more of the sets ofstimulation parameters as optimized sets of stimulation parameters basedon the determined relationship between the motor fiber component and thesensory fiber component corresponding to each cycle.
 14. The medicalsystem of claim 9, wherein: the measurement tool is configured tomeasure the motor fiber component within a first time window; and themeasurement tool is configured to measure the sensory fiber componentwithin a second time window that occurs after the first time window. 15.A medical device, comprising: stimulation circuitry configured to applyelectrical stimulation to a patient; measurement circuitry configured tomeasure a motor fiber component and a sensory fiber component of anaction potential that is evoked from in response to the electricalstimulation; and controller circuitry configured to determine arelationship between the motor fiber component and the sensory fibercomponent.
 16. The medical device of claim 15, wherein the controllercircuitry is further configured to estimate a paresthesia of the patientbased on the determined relationship between the motor fiber componentand the sensory fiber component.
 17. The medical device of claim 15,wherein the controller circuitry is further configured to calculate aratio between the sensory fiber component and the motor fiber component.18. The medical device of claim 15, wherein: the stimulation circuitryis configured to apply a plurality of cycles of electrical stimulation,wherein a different set of stimulation parameters is used in each cycle;the measurement circuitry is configured to measure the motor fibercomponent and the sensory fiber component corresponding to each cycle;and the controller circuitry is configured to determine the relationshipbetween the motor fiber component and the sensory fiber componentcorresponding to each cycle.
 19. The medical device of claim 18, whereinthe controller circuitry is configured to select one or more of the setsof stimulation parameters as optimized sets of stimulation parametersbased on the determined relationship between the motor fiber componentand the sensory fiber component corresponding to each cycle.
 20. Themedical device of claim 15, wherein: the measurement circuitry isconfigured to measure the motor fiber component within a first timewindow; and the measurement circuitry is configured to measure thesensory fiber component within a second time window that occurs afterthe first time window.